Global Navigation Satellite System based tolling: state ... - Springer Link

Netnomics (2012) 13:93–123 DOI 10.1007/s11066-013-9073-9

Global Navigation Satellite System based tolling: state-of-the-art Julia Numrich · Sascha Ruja · Stefan Voß

Accepted: 4 February 2013 / Published online: 1 March 2013 © Springer Science+Business Media New York 2013

Abstract Road pricing or road user charging may be understood as an economic concept regarding direct charges applied for using roads. Different pricing paradigms may be distinguished mainly refering to pricing of congested, non-expandable urban networks as well as pricing of expandable, uncongested (principally, interurban) road infrastructure. Numerous technologies within Intelligent Transport Systems can provide support in efficiently applying various charging mechanisms. Recently, among others, tolling systems have been deployed that rely on the Global Navigation Satellite System (GNSS). The purpose of this paper is to discuss the state-of-the-art of using GNSS technology in road user charging. Keywords Road pricing · Satellite-based tolling · GNSS · Congestion pricing

1 Introduction Charging road users for road usage has been discussed for a long time as a reasonable alternative or addition to taxes [68, 77]. One can argue that the revenues of road user charging or road pricing can be used for maintenance work and building of

J. Numrich · S. Voß () Institute of Information Systems (Wirtschaftsinformatik), University of Hamburg, Von-Melle-Park 5, 20146 Hamburg, Germany e-mail: [email protected] J. Numrich e-mail: [email protected] S. Ruja Q-Free ASA, 7443 Trondheim, Norway e-mail: [email protected]

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new infrastructure. Moreover, road user charging can be used as a means of congestion management. Pricing roads according to supply and demand can help to reduce congestion especially in urban areas and during peak times. In that respect finding optimal prices is an essential topic. However, on one hand congestion may remain if the price is set too low. On the other hand revenues might not be sufficient to fund the scheme if prices are too high. Therefore, careful considerations should be given to the application of different types of pricing schemes (point based, cordon based, zone based, distance based, time-distance based) and the price structure in order to meet the policy objective [6, 11, 14, 30]. The ability to locate and track a vehicle in space and time is becoming more and more fundamental to road user charging. This ability enables the differentiation of a scheme regarding distance, time and place and an implementation on nationwide, high density road networks, including all vehicle and road types [55]. However, technology is not yet mature enough to provide a most sophisticated form of pricing being classified as theoretically perfect [14]. Related technology choice has significant impact on the system infrastructure as well as on operating (toll collection, enforcement) and maintenance costs, flexibility, scalability and the ability to differentiate tolls [14]. In order to establish an electronic toll collection system, which can not be bypassed, area-wide tolling systems are a matter of choice.1 In the beginning of electronic road user charging microwave technology was used for toll highway entrance/exit or toll cordon points. Today Dedicated Short Range Communication (DSRC) microwave is considered as mature and proven technology implemented many times around the world. However, to use this technology high investments in road-side infrastructure have to be made. As the law of diminishing returns applies to road user charging using microwave technology and/or Automatic Number Plate Recognition (ANPR), it seems not necessarily economically useful to install area-wide tolling systems. As a solution to this problem tolling systems have been developed that rely on the Global Navigation Satellite System (GNSS). The purpose of this paper is to discuss the state-of-the-art of using GNSS technology in road user charging. In order to facilitate some common understanding, the functional principles of GNSS are demonstrated in Section 2. Also the different possibilities of using GNSS technology for road pricing are explained. In addition we highlight the advantages and possibilities of the use of GNSS compared to other technologies such as microwave. To ensure the interoperability demanded by the European Union (EU), various standards have to be developed. For this matter the GNSS Metering Association for Road User Charging (GMAR) was founded and it developed the GMAR Performance Analysis Framework (GPAF), which provides a standard for the performance analysis of different electronic toll collection systems. In addition to this work the European Committee for Standardization (CEN) and the International Organization for Standardization (ISO) developed standards that concern GNSS-based tolling systems. These standardization processes are described in Section 2.5.

1 For

a comprehensive survey on road pricing we refer the reader to [77].

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Using GNSS for road user charging imposes challenges, which have to be met in the future. Those challenges and possible solutions are discussed in Section 3. Since the topic of GNSS-based tolling systems has been researched thoroughly, relevant research projects have been selected. Their results are presented in Section 4. To encourage and simplify the use of Intelligent Transport Systems (ITS), the EU laid down a related framework in a directive in 2010, which applies to all information systems used for transport purposes. Since one of the main advantages of GNSSbased tolling is that the technical interoperability can be achieved more easily, the European Parliament and Council passed a directive on the interoperability of electronic road toll systems in the community in April 2004. Subsequently, the European Commission (EC) made a decision on the definition of the European Electronic Toll Service and its technical elements. Those European regulations, as well as the current status of their implementation are briefly portrayed and discussed in Section 5. In Section 6 different implementations of electronic toll collection systems are presented that are currently in use mainly throughout Europe. Final conclusions are drawn in Section 7.

2 Basic principles of tolling technologies Different technologies have been applied for the purposes of electronic road tolling. In this section we focus on the GNSS and provide a survey on related functional principles.2 So far most operable tolling systems rely on the DSRC, which is usually based on microwave or infrared technology. These systems require tolling bridges to be installed along the roadside, as well as suitable On-Board Units (OBU; also OBE) in the vehicle. The toll bridges can communicate with and identify the OBU [6, 27, 82]. The charges are usually calculated by splitting the tolled roads into segments and placing a toll bridge in each segment. The prices for driving through the specific segments are then added and invoiced. Another technology that is used for electronic fee collection is the ANPR, which is based on Optical Character Recognition (OCR). This technology uses cameras to create images of the vehicles. A special OCR software is then used to read the licence plates [6, 27, 82]. Depending on the system these licence plate numbers are then used to either calculate the charges or compare them to a database of registered users. In case the software is not able to detect a licence plate number, the image is transmitted to a data center, where the licence plate numbers are manually checked. We start with some general exposition of GNSS and related applications. Tolling systems relying on DSRC and/or ANPR covering large networks for quite limited number of vehicles have various disadvantages. These can, at least partly, be offset by GNSS-based tolling systems. The advantages of GNSS-based tolling systems are described subsequently and put into perspective also pointing to disadvantages.

2 Besides

the references provided below we also refer to [11, 12, 16, 27, 55, 70].

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2.1 Global Navigation Satellite System GNSSs were developed to allow the determination of positions and navigation on the ground as well as in the air. Today there are two such systems, which are fully functional at a global level. The Navigational Satellite Timing and Ranging (NAVSTAR) Global Positioning System (GPS) is maintained by the United States Government, and the Global Navigation Satellite System (GLONASS) is operated by the Russian Aerospace Defence Forces. Two additional systems, the Galileo positioning system by the EU and the European Space Agency (ESA), and the Chinese Compass navigation system are being planned and shall be fully functional by 2020 at the earliest. The basic concept of a GNSS is similar for all of the aforementioned systems; see, e.g., [38] for a survey of technical details. To assure global coverage 20–30 satellites are needed. Those satellites send out their position data and an atomic timestamp by radio. These are then used by an electronic receiver to calculate its own position. In order to precisely calculate this position, signals from at least four satellites are needed. The receivers’ distance to the satellite, the pseudo-range, can be calculated as follows: (T − Ts ) c where T is the time when the satellites’ signal was received, Ts is the timestamp sent by the satellite, and c is the speed of light. The position of the receiver is determined to be at the intersection of the pseudo-ranges of three satellites. However, this calculation can only deliver exact position data, when the clock of the GNSS receiver is correct. Since atomic clocks are too expensive to be used in GNSS receivers and a very small time error can cause a large error during the position calculation, it is important to consider the time error when calculating position data. This can be achieved by adding a time bias to the actual time data, so that t = T + τ and ts = Ts + τs where t and ts are the clock time of the GNSS receiver and satellite, respectively, T and Ts are the true atomic times, and τ and τs denote the clock bias of the receiver and the satellite, respectively. The position data of the satellite as well as the clock bias of the satellite τs can be obtained from the satellite signal. The position data of the receiver [x, y, z] and the clock bias of the receiver τ have to be determined, leading to four unknown variables, requiring four equations to be solved. Thus four satellite signals are needed to precisely determine the position of the receiver [5]. In 2009 the EU, the ESA and the European Organisation for the Safety of Air Navigation (EUROCONTROL) established the European Geostationary Navigation Overlay Service (EGNOS), which enhances the accuracy of GPS in Europe and is regarded as the predecessor of Galileo. EGNOS uses a network of accurately positioned Ranging and Integrity Monitoring Stations (RIMS), which receive the GPS signals. This data is sent to a master control center, where it is used to calculate integrity measures in combination with the known accurate position of the RIMS.

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These are transmitted to GPS receivers via three stationary satellites. GPS receivers that support EGNOS will then be able to integrate this reliability and accuracy information into their position calculations. In this way EGNOS can increase the GPS accuracy to up to 1.5 m [26]. For an earlier reference analysing GNSS-based tolling using EGNOS findings see [78]. 2.2 GNSS applications and on-board units GNSS can be used for a wide range of applications. These applications can be divided into the following three categories based on the level of reliability that is required [27, 54]: Safety-critical: Applications are safety-critical, when the occurrence of an error can possibly lead to death or physical injuries. An example for this category is the use of GNSS-based systems in air traffic. Liability-critical: Errors in liability-critical applications can result in economical and legal damages. The use of GNSS technology in tolling systems belongs to this category, as an error in the system will not lead to any physical damage but to economical damages. No liability: This category includes all applications, that do not fit the other two categories. For example, this category includes the use of GNSS for navigational purposes as it is done nowadays. As mentioned above the use of GNSS for road pricing is a liability-critical application. This requires the development of such needs to be done carefully and the system integrity needs to be tested intensively before it can be released. Therefore, GNSS-based tolling has been studied thoroughly. Those studies developed different ways to use GNSS for road user charging, which will be presented subsequently. All of these techniques require some kind of OBU to be installed in the vehicles, a data center, and some kind of enforcement system. One way of using GNSS for road tolling is through the use of a thin OBU. Those OBUs are equipped with a GNSS receiver and a Global System for Mobile Communications (GSM) module. The receiver calculates the position of the vehicle and continuously sends the position data to a central data center via GSM, where the correct charges are calculated and the corresponding invoices are sent to the users. In addition to the GNSS receiver and the GSM module, thick or smart OBUs contain memory and a processor. The thick OBU calculates the correct charge onboard. Therefore, the up-to-date pricing data needs to be downloaded from the data center. The position data and the pricing data can be used to determine the correct amount to be charged. This amount is then sent to the central data center via GSM, where invoices are created. Comparing these methods shows that the thin OBU is less expensive for the users. However, it raises privacy concerns, since the position data is sent to the data center and, therefore, enables the generation of movement profiles. Sending the position data to the data center also creates a lot of data volume and requires a continuous GSM connection, because there is no memory space where data could be stored temporarily in case of a connection loss. The cost advantage is countervailed to some

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extent as the data center has to do the calculations and, therefore, is more expensive to maintain. The thick OBU offers a higher degree of privacy, since no position data actually leaves the vehicle. Nevertheless, it still creates a high volume data stream, because current maps have to be downloaded every time a charge is to be calculated. This also limits the degree of interoperability, because when travelling in a new area the correct maps have to be provided for download. This can also raise the costs, since downloading the maps in different countries will usually lead to higher roaming costs. Another plus for the thick OBU is the memory space where data can and will be cached if no GSM connection is available. Nevertheless, the processing unit that is needed for thick OBUs raises the OBU-related costs. Overall neither of those two solutions completely fulfills all demands for a GNSSbased tolling system. There seems to be a trade-off between privacy and cost of the OBU. Also the lower costs for a thin OBU is counterbalanced by high costs for data transfer and the data center. Therefore, the costs are just transferred from the user (thick OBU) to the provider (thin OBU). The Skymeter Corp. [65] proposed a GPS solution using an agile OBU. The agile OBU is supposed to have low costs for the OBU itself, as well as low data transfer costs. This is achieved by calculating position data on-board using statistical methods rather than map-matching algorithms (see Section 2.3.1). Therefore, no maps have to be transferred to and stored on the OBU. Statistical methods are also used to calculate integrity measures and to ensure the correctness of the data. The calculated data is sent to a data center in a compressed form which calculates the charges based on a pricing map [36].3 2.3 Calculating tolls Independently from which OBU is used, there are different methods that can be used to calculate the amount a user is charged. Three methods are presented in the following subsections. 2.3.1 Map-matching algorithms Map-matching algorithms use digital cartography, which includes the charges for specific roads and are updated according to the time of the journey and the type of vehicle. Because of errors during the position calculations simply marking the position data of a vehicle on a map will usually not show the actual position. Therefore, map-matching algorithms were developed. These match the position data with the position data of geo-objects (i.e. roads) on the map to determine which object most likely represents the actual position of a vehicle [61]. However, these algorithms only work when the vehicle is using a road that is marked on the map, therefore,

3 Note

that we are not yet aware of a proper testing of this system.

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requiring complete, accurate and up-to-date maps.4 The estimated real position data of the vehicle is then used to calculate the charges based on the road usage. When these map-matching algorithms come to incorrect results, the user will be mischarged. This is especially crucial in urban areas and when there are roads close to each other, that are charged differently, such as service roads. 2.3.2 Virtual gantries In case that virtual gantries are used, the charge is calculated when the virtual gantry is passed, similar to microwave gantries. However, they do not require roadside infrastructure, as they can be integrated into the digital cartography. They also allow to charge for use of specific road segments when entering and exiting such. When using virtual gantries the tolls are usually calculated for each segment and added up in the end [69]. However, charging a fixed amount when a gantry is passed might cause problems, when they are used for zone charging. These problems occur when a vehicle would ideally have to enter a charged zone multiple times to get to its destination and would, therefore, also be charged multiple times. Users will start to avoid this and use a route that is not optimal, therefore, actually countervailing environmental or economical goals of the toll [33]. Though, this problem is easily mitigated by appropriate processing in the back office or even the OBU. 2.3.3 Pricing grid It is also possible to use pricing grids, which are similar to the grids used in Geographical Information Systems (GIS). These grids contain a different layer for each time slot, where charges are differentiated. However, according to [33, p. 4] the resolution of the grid has to be twice the worst case multipath error. A pricing grid can be used for all kinds of charging schemes. These are more closely described in Section 2.4.2. It is also possible to differentiate charges to the type of vehicle, or emission class, etc. by simply adding more layers to the grid. However, by adding more and more layers the number of layers will rapidly increase. Nevertheless, since this concept has been used in GIS for a long time, there are algorithms to compress these grids in order to achieve a lower data volume. As with other algorithms ensuring a correct charge, it is especially difficult when there are intersecting or parallel roads. For that matter the prices for some grid cell can be set lower or even to zero, while increasing the prices for adjacent cells, where the road choice is more obvious. In urban areas this procedure can lead to priced cells that are set up like virtual gantries, while leaving the rest of the cells unpriced [33].

4 Note that map-matching can cause problems with roads that are temporarily “moved” due

work.

to construction

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2.4 Advantages and capabilities of GNSS 2.4.1 Costs The total costs of a tolling system depend on the number and cost of the OBUs, the cost and amount of the roadside infrastructure and on the complexity of the tolling system [72]. Especially in urban areas the roadside infrastructure can also become a problem of space, if a usage-based scheme is implemented. In particular the design complexity of the tolling scheme and hence the operation strongly impacts the costs of a tolling scheme. To compare GNSS-based tolling schemes with DSRC and/or video based tolling schemes is difficult as the literature on efficiency with respect to operating costs is quite limited (and could even lead to the wrong policy choice [59]). However, the debate about operating costs has recently started in literature and reflects primarily DSRC and video based tolling operations. In the Norwegian context [1] have shown that operating costs varied between 6 and 20 % of gross revenues and [57] mentions that further improvements are possible. Moreover, technology choice obviously matters to improve the efficiency [81].5 Since the use of GNSS technology does not require roadside infrastructure for charging purposes, investment costs for area-wide GNSS-based tolling systems seem lower than for equivalent microwave systems thus making GNSS technology more suitable on a larger geographic scale and for more complex types of charging applications. However, GNSS-based tolling requires some road side infrastructure to be able to enforce detected vehicles that have tampered the OBU [15]. It is also important to consider the effect of interoperability on the costs, as in an interoperable tolling environment the costs for the OBU might decrease [72]. This can be explained by the use of only one OBU for travelling through multiple tolling domains, giving the providers the possibility to produce and sell more OBUs of a kind and, therefore, take advantage of economies of scale. Once technical standards concerning the OBUs are developed, it would also be possible to have them integrated into the car by the manufacturer, thus also decreasing the costs for the OBU significantly [28, 29]. GINA [27] used the results of a Dutch research project to estimate the cost development of different tolling technologies for more complex tolling systems. The 5 For

a discussion of the cost-benefits of the London congestion charge see [48, 60]; Eliasson [18] provides insight into the Stockholm scheme. Economic evaluation issues motivated by the German system are treated in [58]. Following simulations of [37] the focus is on comparing two scenarios where charges are performed either on the OBU and submitted after some threshold value is reached or submitted immediately whenever possible. The operating costs based on GNSS technology for heavy goods vehicles in the EU is estimated to be in the order of 4 billion Euro. If all revenues from tolls from different policy options would be added, operational costs would vary from 12 to 25 % of revenues in EU25 [9]. Walker [80] mentions partially lower operating costs for GNSS-based truck tolling schemes in Europe compared with urban charging scheme; e.g. this is 7 % for Switzerland but more than 25 % for Germany. Though, TollCollect claims that it has lowered its cost to 11 % in 2012 [75]. However, these lower percentages might be partly attributable to the relatively high per kilometer fees that trucks pay and the long distances they travel [14]. The costs of satellite-based regional or national schemes that cover all vehicles are even more difficult to estimate especially since different suppliers propose technology impacting cost estimation leading to significant gaps in the cost calculation [53].

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results show that the more complex a system is, the less cost-effective is the use of DSRC or ANPR technologies. However, the costs of GNSS-based tolling systems do not increase as rapidly, thus making GNSS-based tolling systems more costeffective [27].

2.4.2 Flexibility Using GNSS technology for tolling systems provides the flexibility needed to develop a fair, usage-based tolling system. As demand is continuously changing, different charging schemes can be required in different situations. When using GNSS-based tolling systems these changes in charging schemes can be made quickly without the need for additional technology and equipment, and with low additional costs. There is a number of schemes that GNSS-based tolling systems can be combined with. In general there are two categories of charging schemes, discrete and continuous ones, as described in [34]. Discrete charging schemes are based on certain events that either do or do not occur. A common example of a discrete tolling scheme is bridge tolling. In continuous road charging schemes the toll is based on a cumulative parameter, such as cumulative distance. In practice, however, purely continuous schemes seem to be uncommon as the two kinds of schemes can be mixed and every scheme will eventually contain a discrete aspect at least when leaving a charging domain [34, 73]. Next we display mixed and discrete charging schemes, which are commonly considered for GNSS-based tolling systems. Charges are triggered when a vehicle passes a charging point. These charging points are usually set up as virtual gantries. This scheme is considered a discrete scheme, as there is a specific event that is to be detected and is defining the charge. When using virtual gantries it is important to place them in appropriate places and to consider the correct size, so that it is able to detect all passing vehicles correctly [10]. Multiple virtual gantries can be used to create charging zones by placing them on all possible entries, exits, and throughout the zone. As this kind of charging zone relies on virtual gantries that trigger a charge when passed, it is another example of a discrete scheme [10]. Charging zones are usually used to charge in city centers, where virtual gantries are not a good choice in most cases, as discussed in Section 2.3.2. Also the diameter of the gantries in urban areas would usually have to be bigger than in rural areas in order to avoid mischarging because of multipath errors [33], which are described in more detail in Section 3.1.2. Charging users according to the distance driven is probably the simplest way of charging based on utilization. Since the distance is a cumulative parameter in this scheme, it is considered a continuous scheme [10]. However, a scheme basing solely on distance cannot correctly be used for congestion management, as it does not allow for a differentiation between high and low demand, the time of day, or the type of road used. Distance-based systems are already in place in several countries, which will be portrayed in Section 6.

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A charging scheme combining the driven distance, the time of the trip as well as the location is also suitable for a GNSS-based tolling system [10, 82]. This combination of parameters allows for a charging scheme that adapts to the demand and supply of road infrastructure. It offers the possibility to differentiate so that, for example, charges are higher during peak-times, or in urban areas. This creates incentives for drivers to either drive at a time where roads are not used by that many people, or to switch to public transportation in order to avoid road tolls. As Time-DistancePlace-based schemes are able to adjust to demand, they can be used as a congestion management tool, too [23]. 2.4.3 Adjustment of tolling systems and additional services The fact that no roadside infrastructure is required enables GNSS-based tolling systems to be extended very easily with few or no additional costs simply by expanding the digital cartography used to calculate charges. This way the tolled roads can technically be redefined instantaneously [27, 32, 82]. The same applies to changes in the amount of a charge. Charging schemes can be adjusted to predicted demand or other parameters easily by simply updating the pricing-relevant cartography. Depending on whether the user has to be informed of the exact charges beforehand, charges could even be adjusted to the actual demand in real-time. This enables toll operators to effectively control traffic flow and adjust the demand to the capacities of the roads. Once a GNSS-based tolling system is established, it is easy to integrate different other services, that use the position data of the OBU. These value-added services can be developed by anyone and, therefore, provide many new business opportunities [20]. These value-added services can include automatic emergency calls that also transmit location data, real-time traffic information, as well as Pay-As-You-Drive (PAYD) auto insurance, which is already deployed, e.g., by Hollard in South Africa [39]. 2.5 Standards In order to ensure the interoperability, e.g., demanded by the EU (see Section 5.2), standards have to be developed regarding the business processes and technical solutions. The GMAR has developed the GPAF to standardize performance analysis of GNSS-based systems. In the first phase of the development of the GPAF the focus was on charging reliability. The second phase, which was supposed to focus on security and monitoring, was planned for the end of 2009. However, the standardization processes have been taken over by CEN/TC278.6 When analyzing the performance of GNSS-based tolling systems it is important to distinguish between examination and monitoring. An examination usually takes place before a system is deployed to find errors and generate integrity measures. The

6A

mandate is provided in [21].

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monitoring of a system takes place continuously, while it is in use to detect deviations and also to test performance when rare events occur. As there are no expected values when monitoring a tolling system, it is recommendable to also perform examinations throughout the life cycle of a system. Both aspects, charging reliability and security, can be analyzed from the perspective of the user as well as the toll operator. One may distinguish different scenarios where the system does not charge the correct amount. For instance, when a charging event takes place, but the user is not charged, the user is undercharged at the cost of the operator (Missed Recognition). In another scenario the user is charged for an event that did not take place (False Recognition) [73]. As there is no specific charging event in continuous charging schemes, the charging reliability can not be assessed as easily. Continuous charging schemes constantly create charging errors. These errors are usually quite small and vary, making it possible to generate a distribution function. As mentioned before, charging reliability can be split into charging integrity and charging availability. Without this separation the bias of a charging system could not effectively be evaluated, as it is possible to have a highly accurate charging system, which still tends to overcharge its users. When assessing a continuous tolling system, an interval has to be established in which the calculated charges may vary. This interval constitutes an upper bound, that protects users from being overcharged, as well as a lower bound, which ensures the toll charger from loosing out on charges. This error interval has to be set narrow enough, so that a system will not bias towards overcharging, but on the other hand the error interval also needs to prevent the toll operator from undercharging [10, 34]. Standards regarding electronic fee collection are developed by CEN/TC278/WG1 and ISO/TC204/WG5 in cooperation, who are responsible for standards in ITS on a European and international level, respectively. The development of ISO 17573 is described in [7] as follows. The ISO 17573 uses the Open Distributed Processing (ODP) standard. The ODP standard is based on the concept of different perspectives, the viewpoints, “in order to cover, e.g., hardware components as well as network protocols or interfaces or roles or, in general, policies of the system itself” [7, p. 1]. Those viewpoints define concepts and rules from a partial view of a complete system. There are five viewpoints defined in the ODP standard: the technological viewpoint, the engineering viewpoint, the enterprise viewpoint, the information viewpoint, and the computational viewpoint. However, when using the ODP concepts for the ISO 17573 not all of these are relevant. As the goal of the ISO 17573 is to only provide a framework for electronic fee collection systems, the technological viewpoint as well as the engineering viewpoint may be disregarded. If these two viewpoints were included, the scope of possible implementations would be cut too narrow. As a next step the following classes of roles in regard to a tolling system were defined. These classes are based on the model developed by the CESARE project (see Section 4 and [7, p. 3]). The first class considers the roles related to the provision of the toll service. The second class refers to the roles related to the use of tolling services. The third class of roles are the roles related to the charging, while the last class are the roles related to the management of the toll charging environment. The different roles can transmit information between each other. All classes have a

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specific behaviour. Since some parts of the behaviour of a class can be observed from the outside, these can also be standardized. Especially the interaction between the different roles and, therefore, the information exchanged, as well as the interfaces can and should be standardized. Within ISO and CEN any GNSS-based tolling system falls into a broader category of autonomous electronic fee collection. In autonomous collection systems the OBE is defined to operate without relying on dedicated road-side infrastructure and employs wide-area technologies such as GNSS and cellular CN. ISO/TS 17575, which is a standard with four parts [42–45], defines the application interfaces for autonomous systems. Part 1 defines how charge records are exchanged between a front-end and a back-end. The front-end describes the combined functionality of the OBE and an associated off-board component (proxy); see Fig. 1. The interface between the OBE and the proxy is implementation dependent and is not covered by the standard. Part 2 specifies the application programming interface (API) for use by the front-end system. Part 3 defines the data to be used for describing the individual charging regimes in terms of charged geographical objects, and also the charging and reporting rules. Part 4—Roaming—defines the functional details and data elements required when travelling between several different electronic fee collection regimes. The purpose of this is to ensure interoperability of tolling services such that road users can have one OBE that works in multiple tolling regimes. ISO/TS 12813 [41] defines the short range communication requirements for compliance checking in autonomous systems between an OBE in a vehicle and an outside interrogator such as road-side mounted equipment, mobile devices or hand held units for enforcement purposes. The specification does not apply to compliance checking in DSRC-based charging systems.

Fig. 1 Technical architecture and interfaces (from ISO/TS 17575-1)

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3 Challenges of GNSS-based tolling systems The advantages of GNSS-based tolling systems have already been discussed. However, there are also challenges that have to be overcome, in order to be able to ensure the full operability of these systems. These challenges are discussed in this section. 3.1 Charging reliability Charging reliability addresses the fact, that a toll operator has to be able to prove the correctness of a calculated charge [33]. The reliability of a system is usually split into different dimensions, which depending on the source, usually include: accuracy, availability, continuity and integrity. 3.1.1 Continuity Continuity measures the probability that a system can fully function for a planned period without any unintended interruptions [40, 82]. Continuity is important, as it is the foundation for other performance requirements. As there is no guarantee for complete continuity, tolling system developers have to consider backup systems, in case of a failure of any part of the tolling system. Therefore, it is important to assess the continuity of a system, and also to identify the causes of interruptions [82]. This way measures can be taken to avoid interruptions and to develop backup and emergency systems. 3.1.2 Accuracy Accuracy is described by the average error [40, 82]. The accuracy of a tolling system is important to be able to calculate the correct charge. Especially in urban areas and when different types of roads are priced differently, inaccurate positions can lead to errors in the charging calculations. In these environments low accuracy leads to vehicles being positioned on the wrong roads, and subsequently being mischarged. Especially parallel service roads and motorways are easily detected falsely [6, 40, 82]. In urban areas the vehicles and, therefore, the receivers are usually surrounded by tall buildings. Thus satellite visibility is limited and direct Line-of-Sight (LoS) signals are very few or not existing, lowering the accuracy of position calculation. Furthermore, buildings and other vehicles reflect the signals leading to the multipath effect. Both the LoS signals and the weaker Non-Line-of-Sight (NLoS) signals are picked up by the receiver, but the NLoS signals take more time to reach the receiver. This leads to a decrease in the accuracy of GNSS-based systems [19, 33]. These types of errors have to be considered when implementing any kind of GNSS-based system, as they can also be caused by surrounding vehicles. When using virtual gantries the multipath effect can be avoided by increasing the size of the gantry [19, 33, 79, 82].

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3.1.3 Availability Availability can be seen as the percentage of the overall time that a GNSS-based system is available for use. According to [82, p. 212] the positioning availability is equal to the satellite availability. Since [33] concentrate on a performance measure to be able to compare different tolling systems, they use a monetary charge to assess a system. Therefore, availability also focuses on the charging availability. It is hence defined as the relation of the time a system calculates charges that meet certain performance requirements to the time it is intended to function [33, 40, 73]. As charging availability ensures the functionality of a system it aims at protecting the toll operator from not being able to collect the tolls [34, 73]. 3.1.4 Integrity The charging integrity defines an upper bound for charging errors. Thus charging integrity protects the user from false charges, and is a very important parameter of trust and acceptance [63, 73, 82]. That is, the charging integrity should be kept high, because users are not likely to accept a system that produces a lot of overcharging. 3.2 Interoperability In order to achieve interoperability it is essential to develop OBUs and user interfaces that are compatible with other systems. As the GPS is currently the only globally functioning GNSS, the signals the OBUs receive are the same. This makes it easy to use the same OBU for different systems. However, there are different approaches, as to how the positioning data is used to calculate charges; see Section 2. To achieve interoperability toll operators have to close agreements on how to calculate and collect charges for vehicles using a different tolling system. Since this, depending on the number of included systems, can become a confusing network of numerous contracts, the EU established the European Electronic Toll System (EETS), which avoids individual contracts between all toll operators; see Section 5. 3.3 Acceptance For a GNSS-based tolling system to function correctly its acceptance by the potential users is essential. There are several factors influencing the publics’ perception of a system and, therefore, also its acceptance. The next subsections discuss different important aspects, that influence how well a system will be accepted. 3.3.1 Privacy One critical aspect for a GNSS-based tolling system to be accepted is how the users privacy is protected. Especially when using thin OBUs the position data of the vehicle is continuously transmitted to the data center, so it is technologically possible to

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create movement profiles without the users’ knowledge. A privacy-friendly GNSSbased system architecture using thick OBUs is discussed in [4]. Another approach to ensure privacy is through the use of a proxy, which does not link data with vehicles. One possible solution using proxies is the Anonymous LoopBack Proxy (ALP), which is favored by [31]; see also [46]. The OBU sends encrypted trip data to the ALP, where the correct charge is calculated and send back to the OBU. The OBU can then take actions and send the charge to a data center, or debit a smart card. Since the proxy does not store any data, the journey data stays in the vehicle and may be deleted by the user after payment. Another advantage of the ALP is that the data center does not have access to the proxy, and, therefore, does not have access to the actual journey data. 3.3.2 Fairness An important factor for a tolling system to be accepted, is whether it is perceived as fair. When considering aspects of fairness it is important to distinguish between the fairness of the toll and the fairness of a system. While the fairness of the toll depends on the selection of the charging scheme, the fairness of the systems depends on its implementation. In order to establish a tolling scheme that is perceived as fair, it is important to charge all road users equally [22]. This also includes charging for road use in rural areas, and not only in areas where there is a lot of traffic. However, a fair charging system still calls for a distinction between different classes of vehicles according to environmental aspects. The perceived fairness of a charging system is mainly based on the enforcement system, as this ensures that all vehicles liable to tolling are actually paying the toll. 3.3.3 Enforcement As mentioned before the acceptance of a system also depends on the perceived fairness [47]. However, only implementing a fair charging scheme is not enough. As with all similar fees, an enforcement system is a fundamental part [69]. Ensuring the correct use of the GNSS-based tolling systems as well as the prevention of fraud and tampering can be done using different kinds of enforcement equipment, such as fixed enforcement stations, portable stations or mobile enforcement. Also enforcement can either be done automatically or manually [8, 27]. Fixed enforcement stations can be DSRC-based or ANPR-based gantries that are set up at different points within a network, where there is a high traffic volume and that are not easy to be bypassed. However, there should not be too many stationary enforcement gantries, as they easily offset the cost advantage of not having to install roadside infrastructure. Portable enforcement stations are set up at the roadside and can be moved easily. Portable stations can also use DSRC-based and ANPR-based technologies. They are especially important because users will not be able to deliberately bypass them to avoid penalties. Mobile enforcement is usually implemented by using enforcement vehicles that can be equipped with DSRC-based or ANPR-based technologies to preselect the

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vehicles to be controlled. The enforcement vehicles can either be employed in moving traffic, on the roadside or at gantries or border crossings. The equipment works as a pre-selection and the suspicious vehicles are then stopped to be inspected manually [51]. The enforcement stations can be automated easily. However, especially when using video-based technologies there usually is a manual inspection system as a backup to analyze critical data [8]. When switching from a DSRC-based or ANPR-based tolling system to a GNSSbased system, it is easy to adjust the former system so that it can be used as an enforcement system for the GNSS-based tolling system [27]. 3.4 GSM signals Since the data sent to and from the OBU is usually sent via GSM it is important to consider related costs as well as the signal availability and also the capacities of those technologies. Especially when applying tolling systems to all types of vehicles on all roads the data to be transmitted via GSM will increase rapidly, creating high roaming costs and easily exhausting the capacities of the network. An overload of the cellular network would lead to a decrease in the connection availability. Since the use of GNSS-based tolling systems, and with this the use of GSM networks will most likely increase slowly, telecommunication providers might be able to use the additional revenues to expand their network and thereby absorb part of the increased demand [27, p. 149]. However, tolling systems will have to be developed that are able to cope with weak or even absent GSM signals. This can be done either by caching the data or by reducing the data that needs to be transmitted through GSM. Especially the way software and map data updates are handled can massively influence the amount of data send via the GSM network. Therefore, [27, p. 64] suggests the integration of an USB port.

4 Research projects In the past there have been many research projects studying different aspects of using GNSS technology for road pricing. Some of these are portrayed in this section in chronological order; [27] provides a thorough overview of these projects. A specific project by the European GNSS Supervisory Authority is the Vehicular Remote Tolling (VeRT) project. From 2003–2005 the advantages of EGNOS and Galileo integration as opposed to the use of GPS on its own were analyzed. The results of the VeRT project show that the introduction of Galileo will increase the overall satellite visibility. Especially when the OBUs can use both signals, this will also increase the accuracy in urban areas. The Transport for London (TfL) conducted the Congestion charging technology trials in 2003, which tested different technologies in order to determine, which is appropriate for a congestion-based charging system in London. The project concluded that DSRC technology was most suitable at that moment, but also noted that

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the introduction of Galileo might reduce urban canyon problems to an extent that GNSS-based tolling systems can be used in urban areas. The TfL also found that the OBU technology was not mature enough at the time, but will probably be by the time Galileo is launched. The goal of the GNSS Introduction in the Road Sector (GIROADS) project, which was conducted by the European GNSS Supervisory Authority from 2005–2007, was to study the contribution of EGNOS and Galileo toward the road safety, road maintenance funding, and emission management. The GIROADS project also further developed the concepts of using one OBU for different tolling systems, as well as the use of the OBU for additional services. The Road Charging Interoperability (RCI) project, which was partly financed by the EC and supported by the private sector, studied the aspect of interoperability of GNSS-based and DSRC-based systems throughout the EU. With its work RCI contributed significantly to the further standardisation processes regarding the EETS. RCI results show that clear agreements on roles and technical architecture are needed in order to establish interoperability in the EU. The Active Road Management Assisted by Satellite (ARMAS) project, which was conducted by the ESA within 2006–2009, developed a fundamental architecture for GNSS-based tolling systems, which consists of an in-vehicle-system and a central system outside the vehicle. It recognizes different technologies that may be used for both of these parts. It also highlights the ability of GNSS-based systems to adjust to different charging schemes and to provide value-added services. Another important conclusion of ARMAS is that with the introduction of Galileo as a second GNSS the accuracy will be improved offering a better legal position for toll operators. The European Association with tolled motorways, bridges and tunnels (ASECAP) conducted the Common Electronic Fee Collection System for an ASECAP Road Tolling European Service (CESARE) project, which developed a role model for electronic fee collection systems from 2007–2009. It specified the roles related to electronic fee collection, which were later used during the standardisation process of the CEN/ISO. The GNSS for Innovative Road Applications (GINA) project investigated the use of EGNOS and Galileo for road user charging on a large scale. The project developed and carried out a nation-wide demonstrator of GNSS-based road pricing and additional services in the Netherlands. The demonstration was divided into two phases. The first phase consisted of the exhaustive trials in which two vehicles travelled on pre-determined routes for four weeks using different combinations of GNSS. These trials provided a statistical background of the accuracy and integrity of the system. The second phase, the end-to-end trials, lasted six months and included almost 100 vehicles that drove freely around the Netherlands. These trials were performed to achieve an overall assessment of the system that includes different viewpoints of all stakeholders. Also the end-to-end trials provided data to analyze the performance independently from reference systems [28]. Overall most of these projects came to the conclusion that solely GPS-based systems are not accurate enough at the time to function in urban areas. However, the integration of EGNOS and the introduction of Galileo are expected to change this significantly.

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5 European regulations As the establishment of the European Economic Area and the economic growth of European countries led to higher transport volumes, the congestion of European roads increased as well as the energy consumption and, therefore, the environmental impacts. Trying to solve these problems the EU is encouraging the implementation of electronic tolling systems, by setting regulations and standards for the development and implementation of such. Recent regulations mainly focus on achieving interoperability throughout the Union. The directives relevant for GNSS-based tolling systems are discussed in the following. 5.1 Intelligent transport systems directive The Intelligent Transport Systems ITS directive [25] sets a framework for the deployment and use of ITS within the Union [25, p. 3]. The directive defines ITS as “systems in which information and communication technologies are applied in the field of road transport, including infrastructure, vehicles and users, and in traffic management and mobility management, as well as for interfaces with other modes of transport” [25, p. 4]. According to this definition the directive also applies to GNSS-based tolling systems. The directive defines four priority areas for the development of specifications and standards. These priority areas are also related to GNSS-based tolling systems [25]. These priority areas concern: (1) the optimal use of road, traffic and travel data; (2) continuity of traffic and freight management ITS services; (3) ITS road safety and security applications; (4) linking the vehicle with the transport infrastructure. As with toll collection each member state may decide upon the deployment of ITS applications. However, where ITS services are deployed the member states have to apply them according to the principles, which are laid out in Annex II of the directive. In the following the relevant principles and their application in GNSS-based tolling systems are presented. Be effective: Efficiency is defined by the directive as making “a tangible contribution towards solving the key challenges affecting road transportation in Europe” [25, p. 13]. In general road pricing can contribute to these challenges because it helps reducing congestion and emissions by making users aware of the social costs of driving. As GNSS-based tolling systems can be applied area-wide the shift in traffic flows to circumvent charges can be avoided. Be cost-efficient: Effective costs for GNSS-based systems are comparably low in relation to the use of such. The costs of GNSS-based tolling systems have already been described in Section 2.4.1. Be proportionate: Local, regional, national and European features can be taken into account when establishing a GNSS-based tolling system. It is also possible to adjust GNSS-based systems easily to changing conditions. This has already been discussed in Section 2.4.3. Support continuity of services: Seamless service can be ensured across the EU, since GNSS signals are available beyond borders. Especially the EETS, which

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is described in more detail in the next section, shall be able to ensure continuity in the future. It is also theoretically possible to expand GNSS-based charging systems and the EETS beyond the borders of the EU as well, since there are no technological limitations. Deliver interoperability: Interoperability between GNSS-based charging systems is technologically easy to establish. However, there has to be a contractual network in order for users to be able to use the same OBU in different countries. Also the toll providers have to come to an agreement on how to charge users for driving in other countries. The EETS directive and commission decision, which are portrayed in the next sections, set a basic framework to achieve interoperability of all tolling systems within the EU. Support backward compatibility: When establishing interoperability it is important that users and toll operators are able to continue the use of their existing systems. Therefore, any new technology or device also has to be compatible with these older systems, while still allowing for technological progress. This aspect is also defined in the EETS directive and the Commission Decision on the EETS. Support maturity: The maturity of a GNSS-based tolling system needs to be demonstrated in order to achieve acceptance. Also the possible risks, that come with the public introduction of such a system, need to be assessed beforehand. These demonstrations have been and are being conducted through different research projects, which have been portrayed in Section 4. Deliver quality of timing and positioning: Since the OBUs used for GNSS-based tolling systems all contain a GNSS receiver, continuous timing and positioning can be guaranteed. The accuracy of this data depends on the environment, but is expected to be improved with the introduction of Galileo; see Sections 3.1.2 and 4. 5.2 EETS directive The EETS directive [24] requires all road tolling systems in the EU to be able to communicate with all others. Therefore, it requires all newly deployed tolling systems, starting January 1, 2007, to use either satellite positioning technology, mobile communications technology using the GSM-GPRS standard and 5.8 GHz microwave technology [24, p. 1] or a combination of these. However, it recommends the use of satellite positioning and mobile communication technologies. Where tolling systems are already in place measures should be taken to ensure that “at least 50 % of traffic flow in each toll station can use electronic toll systems” [24, p. 4]. Furthermore, the directive sets up an EETS, which shall include all electronically priced roads in the EU. The EETS shall make it possible for the user to close only one contract that permits access to the whole network of roads. Any EETS provider shall accept all user’s subscriptions “irrespective of the place of registration of the vehicle, the nationality of the parties to the contract, and the zone or point on the road network in respect of which the toll is due” [24, p. 5]. The directive requires member states that already have electronic toll collection systems, to ensure the availability of EETS for Heavy Goods Vehicles (HGV) at the latest three years after the commission’s decision, and for all other vehicles at the latest five years after the decision.

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Additionally the directive initiated a report of the EC about the possible migration from other technologies to the allowed technologies. The report shall also include a study of the use as well as a cost-benefit analysis of the utilized technologies. The EETS directive stipulated that the EETS is to be defined by a decision of the EC in accordance with an Electronic Toll Committee. This decision is discussed in the next subsection. 5.2.1 Decision on the EETS The commission’s decision on the EETS [22] lays out technical specifications and requirements as well as contractual rules relating to EETS provision [22, p. 3]. It requires all EETS providers to register in a member state. In order to be eligible for registration they have to meet certain requirements, including amongst others EN ISO 9001 certification or equivalent [22, p. 4], proof of “competence in the provision of electronic tolling services or in relevant domains” [22, p. 4], proof of technical equipments [22, p. 4], and adequate financial capacities. The decision obligates all EETS providers to close contracts covering all EETS territories within 24 months of their registration. They have to provide appropriate service and technical support [22, p. 4] to their users. They also have to provide the EETS users with invoices, that clearly separate service charges from tolls, and also show details as to where and when tolls incurred and their composition. Toll chargers have to accept any EETS provision request without discrimination. The member states have to ensure that EETS is provided as a single continuous service [22, p. 6], meaning that no further in-vehicle human intervention [22, p. 7] is needed during a journey and also that interaction with a particular piece of on-board equipment [22, p. 7] stays the same in all EETS domains. In order to ensure interoperability and backward compatibility the commission’s decision establishes requirements for all components that the interoperability depends on. The decision also initiated a report of the EC on the progress of the implementation of the EETS, which is discussed in the following subsection. 5.2.2 Implementation of EETS A report on the implementation of EETS [23] states that “the European Electronic Toll Service is not yet a reality in everyday life of road users” [23, p. 4]. According to the report, until 2009 member states introduced electronic tolling systems disregarding the regulations set by the EETS directive, especially not regarding the timescale. Most member states also failed to implement the legal framework for EETS. According to the report at least one potential EETS provider was denied registration because of this. This can also be seen as a reason for the fact, that so far no EETS provider has been registered in any member state. As the EETS providers are a substantial part of the EETS, because they close the contract with the users and supply the necessary equipment, this is important when analyzing why the EETS has net yet been established. However, there are organisations that are willing to register as EETS providers. About ten of these have formed the Association of Electronic Toll and Interoperable Services. It also seems likely that with the extension of road char-

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ging, which according to the report is already planned in three countries, a market for EETS will open up.7 Even though the EETS is not yet in place, measures have been taken to comply with the European regulations. These measures include the establishment of registers of EETS domains and EETS providers of the member states. Also according to the report manufacturers are requesting additional information from the EC, and negotiations between potential EETS providers and toll chargers have started [23, p. 6]. To push the further implementation of the EETS the Commission will take certain measures, which include infringement procedures, if member states do not fulfill the requirements of the EETS directive. The commission will also set up a network of national conciliation bodies [23, p. 8]. Some toll chargers tried to set clauses that automatically end the contract with an EETS provider, if there is no complete EU coverage. As such clauses create additional entry barriers, the Commission will not allow them and is considering infringement procedures. The commission also plans to set up a comprehensive information sharing resource platform [23, p. 8] to promote the exchange of information on EETS among professional stakeholders [23, p. 8]. In addition to the reports that have been prepared by the European institutions, [35] did a cost-benefit-analysis of the regulations concerning the EETS. They compare the direct cost advantages of EETS for users (i.e., the benefits of not having to deal with manual payments [35, p. 4] and “having [...] fewer OBEs, contracts, and invoices” [35, p. 4]) against the additional costs for the provider to achieve interoperability (i.e. the cost of supplying OBUs that function with multiple systems, the cost of creating a data center working with multiple systems, and the cost of reaching contractual agreements with all toll operators). Their extensive calculations lead to the conclusion that the current regulations concerning the EETS would not lead to positive net benefits, but will rather lead to a social deficit. They also found that every kind of mandatory interoperability will most likely always create a net loss and will, therefore, not be implemented completely unless they are financed publicly. They developed the four following general suggestions for policy makers to increase the level of interoperability, while producing a net benefit: Interoperability Radius: Policy makers shall focus on a radius in which a certain degree of interoperability is to be achieved rather than on complete interoperability. This concept would most likely lead to the creation of interoperability clusters, especially for major transit routes. Even though there still would not be a unique

7 The

19th ITS World Congress in Vienna in October 2012 provided a platform for a ‘Special Interest Session’ to discuss implementing the EETS as well as to highlight some of the current challenges. Consensus of a panel with stakeholder representatives and the audience was that fully implementing EETS would take a long time (up to ten years) and only really make progress if there was a new initiative to galvanize all relevant stakeholders to work collectively toward implementation. See also [50] for a recent comment on this discussion.

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OBU all across Europe, it would reduce the number of OBUs needed when travelling through Europe. Nevertheless, this concept does somewhat defeat the goal of the EETS to be able to use only one OBU all over Europe independently from how profitable the route might be for toll chargers. Limited Technical and Procedural Designs: By setting the regulations so narrow, that there is no possible variation of the implementation, interoperability is achieved almost automatically and with low costs, as the toll operators will not all have to develop their own solutions to the technical and procedural questions. However, [35] themselves noted that this is not likely to pass in the EU as it might infringe on the national sovereignty. Limit Points of Negotiation: As the contractual agreement causes a large part of the costs, it is suggested to reduce these by “harmonising specifications for service level requirements and terms & conditions” [35, p. 16]. However, in order to establish an open market for EETS providers, these specifications should be limited as not to distort price mechanisms. Clusters: Another possibility to reduce the costs of contracting is seen in encouraging clustered negotiations. EETS providers might be able to delegate their negotiation power. Since this would lead to few representative parties negotiating with toll chargers, the number of contracts would be lowered significantly.

6 Current practice This section presents examples for the practical implementation of tolling systems in different countries using different technologies. As the interoperability between different tolling systems in Europe was discussed earlier, European tolling systems are portrayed. Also the focus is to show the variance and combinations of technologies used. Therefore, some tolling systems are not included, as they use the same basic function as others. For example, the Stockholm congestion tax is not presented as it relies on a similar technology as the London congestion charging zone and the Gothenburg congestion charge.8

8 Note

that GNSS-based charging currently applies only to trucks above 3.5 t and 12 t, respectively. In Stockholm we observe a cordon based video tolling system which runs with much lower operational costs as a share to the yearly revenue compared to London which is an area based video system that enforces vehicle registration numbers at 180 sites, covering entry/exit points and places within zone. Currently, several European countries consider the implementation of road user charging schemes that are more ambitious in terms of geographical scale, scope and level of differentiation. The most specific example is Belgium (see [52]) where it is planned to implement a nationwide distance-based scheme for trucks on specific roadways (per km) differentiated towards time, place and vehicle characteristics, as well as a time-based charging system for all light vehicle users. Another example is Denmark (see [13]), where the implementation of a distance-based road user charging scheme is considered for trucks above 12 t on specific roads, and differentiated to vehicle class. Also Hungary, Slovenia, Russia and Finland have been putting GNSS-based road user charging schemes on the agenda.

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6.1 Swiss performance-related heavy vehicle fee Switzerland introduced a performance-based toll on January 1, 2001. The toll applies to all vehicles above 3.5 tons permissible total weight on all Swiss roads. The amount of the toll depends on the distance driven on Swiss roads, the permitted gross weight and the emission standard of the vehicle. All Swiss vehicles are required to have an OBU installed by a service partner, while all foreign vehicles have the option of choosing between installing an OBU or using an ID-card. When entering Switzerland the OBU is activated automatically by a microwave connection. The OBU is connected to the odometer in order to determine the driven distance. It also includes a GPS receiver and a motion sensor, which can be used to control the data received from the odometer and, therefore, help to prevent fraud and manipulation. Swiss users have to transmit the collected data once a month. This is done by inserting a smart card to the OBU. The data is then copied onto the card. The user can either send the card itself to the data center or use a computer to read the data and transmit it electronically. If a foreign user decides to use an OBU the data is transmitted automatically each time when exiting the network and the user will be billed once a month. Foreign users not using an OBU have to register at a station terminal at the first entrance. The user data and vehicle data are saved into a database and the user is given an ID-card. Each time when entering the driver will have to use a station terminal and enter the ID-card, the current mileage and the type of trailer. The user is then given a receipt in duplicate. When leaving the country the user has to provide one of the receipts, as well as the new mileage, so that the correct toll can be calculated. The Swiss tolling system relies on a combination of fixed and mobile enforcement. The fixed enforcement stations read out the data of the OBU via DSRC and compare it with electronically gathered measurements such as the license plate number. In addition the police patrols also combine their regular controls with toll enforcement. The mobile enforcement can be done easily as the OBU contains a light-emitting diode (LED), which allows to determine from a distance whether the OBU is operating and set up correctly [64]. 6.2 London congestion charging zone The London Congestion Charging Zone (CCZ) was introduced on February 17, 2003 [76]. Anyone driving within the CCZ, which is the city center of London, between 7am and 6pm monday through friday has to pay a daily Congestion Charge of £10. The CCZ uses a network of 650 cameras at 180 sites on entries, exits and within the zone. The cameras, using ANPR, still take pictures of both the licence plate as well as the vehicle. Once the licence plate number is read, the system checks the database, for possible discounts, exemptions, and automatic payments. If these exist, the pictures are deleted right away. If there is no exemption and no automatic payment found in the database, the vehicle owner is looked up via the vehicle registration and is billed the daily charge.

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6.3 Austrian truck toll On January 1, 2004 Austria introduced a distance-based tolling system on all motorways and expressways. The toll applies to all vehicles above 3.5 tons permissible total weight and depends on the number of axles and on the emission standard. In comparison to other European countries the Austrian toll does not draw a distinction between commercial freight transport and other transports. The Austrian tolling system is based on DSRC microwave technology. Therefore, toll bridges where installed on all tolled roads. All users have to install an OBU in their vehicle, which can then communicate with the toll bridge, so that the correct toll can be calculated. The enforcement system includes about 100 enforcement stations. Each enforcement station consists of one enforcement bridge, that determines the number of axles and communicates with the OBU via DSRC, and one enforcement bridge that uses cameras to determine the licence plate number of the vehicle, and transmits critical images to the data centers. In addition to the stationary enforcement there are portable enforcement stations and mobile enforcement teams. In case of fraud or incorrect payment, there is the possibility to pay a substitute toll of up to e220. Only if this substitute toll is not paid in time, there will be a penalty of up to e3,000 [3]. 6.4 German TollCollect The German HGV toll was introduced on January 1, 2005. The toll applies to all commercial vehicles with above 12 tons permissible total weight. The amount of the toll is determined by cumulative distance, axles, type and emission standards of the vehicle. On introduction the toll was only applied to vehicles using motorways, but since the toll caused traffic to move to non-tolled roads, certain federal roads were steadily added to the network of tolled roads. Before using tolled roads all vehicles have to log-in to the system. There are different ways to do this. Most vehicles use the automatic log-in based on a GPS-based OBU. In order to be able to use automatic log-in the vehicle and the company have to register with the service provider TollCollect. The OBU has to be installed by a service partner. The relevant fixed vehicle parameters as well as the position data of all tolled roads are saved on the OBU. When starting a journey the driver will have to start the OBU which will then recognize when driving on a tolled road and automatically save the GPS data and supplementary position data. Upon completion of the journey the OBU calculates the amount to be charged and transfers it to the TollCollect billing center via GSM. Alternatively to the automatic log-in users can register with TollCollect and login online. In the process the start time and route will have to be entered. This data is then used to calculate the start time and the latest end time of the journey, which also limits the validity of the log-in receipt, that drivers have to carry with them in the vehicle during the journey. The third alternative is logging in at a toll-station terminal. This method can also be used by unregistered users and vehicles. The procedure is similar to the procedure when logging in online.

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The payment of tolls is enforced using automatic toll enforcement gantries, as well as mobile manual enforcement, and manual enforcement teams in combination with the fixed tolling bridges [74]. 6.5 Slovakia In Slovakia a functioning GPS based tolling system is in place since January 1, 2010. All vehicles above 3.5 tons permissible total weight have to pay tolls electronically when driving on certain sections of motorways, expressways and selected first class roads. 2,400 km of roads are tolled. Before using the electronic toll collection system drivers have to register their vehicle and obtain an OBU at one of the distribution points. The electronic toll is enforced by the toll police. If someone is found not paying the toll at all or correctly, the driver can be charged with a cash penalty of up to e1,300. If the charges and fines are not paid the toll police may take away the licence plates and registration of the vehicle. The tolled roads are divided into segments. The OBU uses GPS technology to determine, when a vehicle is located on one of these segments. The charges are then calculated according to the segments that have been used. The toll can either be paid in advance, or post-paid via an invoice. Nevertheless, there still is the possibility of paying the toll without the installation of an OBU. The so-called ticketing is available for all transit hauliers. When entering Slovakia drivers will need to provide information about the vehicle and select a transit route. The toll will then be calculated and paid based on this data. Ticketing was first introduced on January 12, 2010 and was available for 18 transit routes. Initially it was only available till March 31, 2010. However, the ticketing period was extended several times while decreasing the number of available transit routes. As of now it will be available on four transit routes until December 31, 2012 [66, 67]. 6.6 French Eco-tax The French government is planning on launching the Eco-tax in July 20, 2013, after an experimental phase in Alsace starting in April 2013. The French Eco-tax will be applied to all vehicles above 3.5 tons permissible total weight. The 15,000 km taxable road network will contain state-owned motorways and highways, as well as departmental roads. Every vehicle using taxable roads in France will have to have an OBU, that is equipped with a GPS receiver. The taxable network will be divided into sections, which are marked by pricing points. These pricing points act as a virtual gantry, and will, therefore, be placed between intersections. When a pricing point is passed the tax will be charged. Automatic fixed enforcement gantries will be placed throughout the network, as well as automatic mobile enforcement, that will be moved around different parts of the network. Both systems can detect users without OBUs, and will take pictures of these, which are then reviewed by the data center. In addition to the automatic enforcement option there will also be the possibility for French authorities such as the police to control drivers.

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There will be a fine of up to e750 for not paying the Eco-tax correctly, as well as the immobilisation of the vehicle [2, 49, 62]. 6.7 New Zealand There are very few examples for GNSS-based charging schemes beyond the borders of Europe. In New Zealand heavy good vehicles above 3.5 tons are charged according to the distance driven. The use of electronic equipment to record road usage is a voluntary alternative to an already existing paper based system which became fully operational in 2010 [56]. 6.8 Congestion tax in Gothenburg The latest congestion charging scheme becoming operational in the European charging arena is the congestion tax in Gothenburg. This tax, also referred to as the Gothenburg congestion charge, is a tax levied on most vehicles entering and exiting central Gothenburg, including some main roads passing by the city. The congestion tax was successfully introduced from January 1, 2013, with the Stockholm congestion tax as a model, and consists of 42 charging points [71]. 6.9 Achieved interoperability So far there are only few interoperable tolling systems in Europe. One example is the Austrian tolling system. It is interoperable with the Swiss and the German system. The technological changes to fulfill the requirements of the EETS directive were made in 2008. However, the Austrian toll system has been interoperable with the Swiss system from the start. To use the Austrian tolling system Swiss users have to file a contract with the Austrian toll operator. The Swiss toll operator will then be notified and the user will receive a smart card, which can be inserted into the Swiss OBU. The charges for both countries can then be calculated and billed separately [3]. Another example for interoperable systems is the EasyGo project, which allows for the use of selected tolled roads, bridges, tunnels and ferries in Norway, Sweden, Denmark and Germany with only one OBU. All customers of the included service providers, which also have an OBU installed in their vehicle, will automatically be charged correctly, when using routes outside of their original tolling system. In comparison to the Toll2Go service it is important to note, that users will not be invoiced separately, but will get only one invoice from their original toll charger, which also lists all journeys in other tolling systems [17, 23]. This implementation of interoperability is similar to the EETS. Since September 1, 2011 the Austrian toll can also be calculated and charged by using the German TollCollect OBU. Users must have a contract with one of the toll operators and register for the Toll2Go service. After the registration has been approved by the Austrian toll operator, the TollCollect OBU will be activated, or installed if it has not been done before. The OBU then automatically calculates tolls in both countries. As with the Swiss-Austrian system the charges are billed separately.

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The Toll2Go service is especially important, as it is the first functioning example of a cooperation between a microwave-based and a GNSS-based system [3, 74].

7 Conclusions and future developments In this paper we have surveyed GNSS-based tolling systems and their related impact and implications. In conclusion these systems can provide many advantages compared to former electronic toll collection systems or vignette systems. GNSS-based solutions offer possibilities to employ charging schemes, that are not available for other systems. The low costs for expanding a GNSS-based system allow to employ area-wide tolling systems. This is especially important as an area-wide system can help to prevent from possible traffic rerouting, which may cause serious environmental and social problems. Once a GNSS-based tolling system is established, the OBU can be used for additional purposes. The value-added services create many opportunities for new business projects. As the users will also profit from these services, this might become an additional incentive to install an OBU. Even though there are many advantages of GNSS-based tolling systems, there still are technological challenges that have to be overcome in order for such systems to be employed successfully. One of these challenges is the accuracy of GNSS signals in urban areas. Recent research projects concordantly concluded that the accuracy of GPS on its own is not good enough to provide a legally binding basis for toll collection. They also concurred that the integration of both EGNOS as well as Galileo will be able to reduce urban canyon problems and overcome the challenge of accuracy. Another challenge might occur regarding the availability and the capacities of GSM. This might especially become more important as tolling networks grow and the number of users increases. It might be resolved, if telecommunication companies upgrade their networks according to the demand. As they will receive additional revenues from offering services for GNSS-based tolling this would also be economically justified. Nevertheless, OBU developers should also include the technical necessities to store or transfer data without using cellular networks. This aspect also needs to be considered when standards are developed. Since GNSS-based systems constantly calculate the position of the vehicle, it is easy for toll chargers to create and use individual movement profiles. There are different possible solutions to ensure the European standards on privacy and the processing of personal data. When using thick clients the topic of privacy becomes less crucial as the position data does not have to leave the vehicle. Nevertheless, privacy concerns need to be addressed especially in architectures using thin clients. A possible solution in these cases is the use of proxies, which calculate the correct charge without the need for identification of the user. However, it is imaginable that value-added services need to enquire the users’ consent to collect and use (individual) position data. Therefore, there also needs to be a secure possibility to transfer movement data to authorized data centers via cellular networks. This must be done by encrypting the data using up-to-date encryption

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technologies. This way only the toll operator, or legitimate value-added service providers will be able to use protected data. Another challenge of GNSS-based tolling, which has the potential to become a big advantage especially compared to other tolling systems, is the interoperability. For other electronic tolling systems achieving interoperability can be hard. However, it is technologically easy to establish interoperability between different GNSS-based tolling systems. Nowadays interoperability is still just a concept, and also demanded by the EU, but has yet to be implemented area-wide. In order to establish a fully functioning system it is important that all involved stakeholders agree on certain standards regarding the business processes, the technologies used as well as the information transfer between systems, users and operators. In order to achieve interoperability it is important to consider the contractual regulations. Since the establishment of the EETS requires EETS providers to close contracts with all toll operators, there is a need for a contractual framework to avoid every toll operator negotiating about every detail with every other toll operator. Such a framework would be able to decrease the costs of achieving interoperability. Although the cost-benefit analysis referred to in Section 5.2.2 does result in a net loss if complete European interoperability has to be achieved, it does not consider the possible future developments of the EETS. Once GNSS-based tolling systems are fully functional it does seem economically sensible for more countries to extend their tolling networks rather than increasing taxes. This would be pushed further forward by the EETS and would set incentives for drivers to reconsider their driving behaviour, thus leading to positive environmental effects, which have not been considered in the analysis. Overall there has been a steady development and research in the field of GNSSbased tolling systems. Although the technological concepts are mature enough, there still is a need for practical improvements and implementations, especially in the fields of accuracy, standardisation, and interoperability. The accuracy of GNSS-systems is likely to be large enough to ensure charging reliability once Galileo is functional. The standardisation is undergoing a steady development. Once the necessary standardization processes are finished it will also be possible to practically implement the interoperability all across Europe.

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