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sectors—stretching in length from 4 to 9 km—of the motorways A92 (Munich North). M90/A90 (Edinburgh) and A4 (Verona). A series of field trials have been ...
EVALUATING THE EFFECTIVENESS OF ROAD INFORMATION AND WARNING SYSTEMS: THE COMPANION EXPERIENCE

Danilo Fum Department of Psychology University of Trieste fum @univ.trieste.it

Gilberto Tognoni Autostrada Brescia-VeronaVicenza-Padova SpA [email protected]

SUMMARY The paper reports the results of two experiments devoted to evaluate the efficacy of Companion, an information and warning system deployed on a tract of the Italian A4 motorway. Relying on the findings of previous studies, performed within the framework of the European projects INFOTEN and TABASCO, the experiments were devoted to identify those factors that are critical in determining the efficacy of the system, and to contribute to the elaboration of guidelines that will help motorway operators in their day-to-day use of the system. In the first experiment, in which an incident to a truck was simulated, the effects of the warning distance and of the flashing pattern were stressed. The results of the second experiment, in which Companion warned the drivers about a lane closure, suggest that it is important to take into account the scenario in which the system is utilized.

INTRODUCTION The last decade has seen the introduction on roads and motorways of an impressive array of new technologies aimed at improving traffic safety. In particular, various systems have been brought into use which try to reduce driving risks by alerting people about dangerous or anomalous conditions (e.g. queues, accidents, fog, ice, etc.). While there is a general agreemeent about the need to intensify any effort towards safer driving, very few attempts have been made to assess the efficacy of these systems, and to estimate the real return, in terms of improved safety, of their deployment. A notable exception to this situation is constituted by the studies that have been performed—within the framework of the European projects INFOTEN and TABASCO—to evaluate the technical functionality, the impact on traffic, and the acceptance by users of Companion. Companion is an information and warning system designed to alert drivers about any unexpected event constituting a potential danger. The system utilizes roadside electronic guide markers that emit yellow or orange signals according to various possible flashing patterns. It has been installed on sectors—stretching in length from 4 to 9 km—of the motorways A92 (Munich North) M90/A90 (Edinburgh) and A4 (Verona). A series of field trials have been previously

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carried out with Companion in Bavaria and Scotland (1) (2) (3). Among other things, it was found that, when the system was activated, the following results could be obtained: • A reduction in vehicle speed, in the range of 10-20%, and dependent on the site, initial speed, flow level and time of day. • Harmonization of traffic speed between lanes. • An increase in vehicle headway and a reduction in the number of vehicles following at a critical distance. • The perception among motorists that the system could increase their safety and reduce accident likelihood. No evidence, on the other hand, was obtained suggesting that the system could cause lane changing or other dangerous behavior. The paper reports the results of two evaluation experiments performed on the Italian site of Companion. The Department of Psychology of the University of Trieste—on behalf and with the active cooperation of the Autostrada Brescia-Verona-VicenzaPadova SPA, which manages the A4 motorway sector (from Montebello to Soave) where Companion has been deployed—carried out the experiments. Relying on the previous findings, the experiments were devoted to identify those factors that are critical in determining the efficacy of the system, and to contribute to the elaboration of guidelines that will help motorway operators in their day-to-day use of the system. More particularly, the experiments tried to find an answer to the following questions: 1. Is there any difference in the efficacy of the system depending on the warning distance? It could be hypothesized that there exists an optimal interval for the system to be maximally effective. An earlier warning could not be taken into account by the drivers, while a warning lasting too long might be perceived as a false alarm, and will not be able to produce the desired results. 2. Is there any difference in the efficacy of the system depending on the light pattern (frequency, pulse/pause ratio, color, etc.) according to which the warning signal is delivered? There is a high degree of flexibility in the conditions according to which the system can be utilized but, up to now, no clear criteria have been devised to choose among the various settings. 3. Is there any difference in the efficacy of the system according to the kind of dangerous situation it warns drivers about? It could be hypothesized that the drivers’ behavior could vary, being influenced by the perceived nature of the risk. All the previous evaluation studies examined exactly the same situation (a simulation of a truck breakdown). It was considered therefore worthwhile to assess the efficacy of Companion in a broader range of settings.

EXPERIMENTAL DESIGN AND METHODOLOGY In the first experiment, a replication of the scenario adopted in Munich and Edinburgh was adopted. The scenario simulates a breakdown occurred to a truck that has been forced to stop on the emergency lane, and constitutes therefore a potential danger for people driving along the motorway. Working under the scenario assumptions, a series of trials—each lasting one hour—have been carried out according to the following schedule:

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Table 1: Phases during each trial of Experiment 1 Minutes 00’-15’ 15’-30’ 30’-45’ 45’-60’

Description Traffic flows regularly: Companion off Truck resting in the emergency lane: Companion off Motorway personnel comes to help: Companion on Accident cleared: Companion on

Condition BASE EMERGENCY ACTIVATED ALERT

The first fifteen minutes of every trial were devoted to collect some baseline measures while the traffic was flowing undisturbed. After this period, a truck stopped just in front of a small resting area (but remaining completely on the emergency lane) simulating a mechanical incident. The truck activated the hazard warning lights, and alert signals were put on the lane. After another fifteen minutes, a patrol car with motorway personnel came to help and requested the activation of Companion. Incident clearance occupied another fifteen minutes. After that, the truck left the resting area and the surface signals were removed. Companion was left on for the remaining part of the trial allowing the collection of data while the system was operational but no hazard was present on the road. A 3 x 2 factorial design was employed which manipulated, as independent variables, three different warning distances (250m, 500m, and 750m) by two different flashing patterns (an up-down stroboscopic effect and a funnel effect, respectively). Thee speed of the vehicles running along the three motorway lanes was the dependent variable. Speed was measured through magnetic loops installed on the lanes at km 87.4 of the section Montebello-Soave of the A4 motorway . All the measures were taken 200m before the point where the simulated incident occurred (at km 87.2). The warning distances refer to the span between the beginning of the flashing lights and the location of the measuring loops. The lights, however, continued to be kept flashing up to and beyond the point were the truck was located. The experiment was carried out on the 6th and 7th October 1998. A series of 12 trials were performed with data collected twice for each condition. Due to transmission problems with the magnetic loops devoted to recording vehicle speed, however, data for only eight trials resulted available at the end of the session. Fortunately, all the six experimental conditions were tapped by at least one trial with two conditions (250mfunnel and 500m-up/down) covered by two trials. The second experiment was carried out on the 14th-16th October 1998. In this experiment a different scenario was adopted with the goals of: • studying the efficacy of Companion while the system was operating in a potentially dangerous situation (motorway lane closed for works) which was different from that examined in the previous trials and in the Munich and Edinburgh sessions, and • assessing the interaction between the warnings delivered by Companion and through a traditional VMS system.

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During the experiment, the overtaking lane was closed exactly at the same location (km 87.2) previously utilized as the resting point for the truck. Alert signals were placed on the lane starting 500m before the obstacle, while measuring loops situated 200m upstream recorded the speeds of the vehicles passing through. A VMS panel, located 10km before the critical point displayed appropriate messages. Two different variables were manipulated according to a 4 x 2 factorial design: the Companion status (off vs. on, and in this latter case with a 250m, 500m or 750m warning distance) and the saliency of the messages delivered through the VMS panel (a neutral message vs. a salient message alerting the drivers about works on the lane). No difference in the flashing pattern was introduced. In the experiment 24 trials were performed, eight trials per day, one for each experimental condition. The experimental conditions of each day were varied randomly. The data of all the trials were available for the successive analysis.

RESULTS OF EXPERIMENT 1 A preliminary issue we wanted to examine was whether Companion had any general effect in modifying the driver’s behavior, more particularly in reducing speed. Data collected when Companion was off (Base and Emergency conditions) vs. on (Activated and Alert conditions) were compared. The activation of Companion, as such, did not have any general effect on the vehicles’ speed: there was only a very small (about 1 km/h), absolutely non-significant difference, between the two settings. Table 2, which reports the means for the separate trial conditions, corroborate this conclusion. Table 2: Vehicle mean speeds under different trial conditions. Condition BASE EMERGENCY ACTIVATED ALERT

Mean 112.8 109.5 110.8 113.4

St. Dev. 20.59 21.86 20.68 19.84

St. Err. 1.25 1.33 1.26 1.21

Another factor was, on the contrary, influential in determining the drivers’ behavior—independently from the activation of Companion—and it is constituted by whether a truck was (or wasn’t) standing on the emergency lane. By comparing the results of the Emergency + Activated conditions (i.e. truck present) vs. the Base + Alert ones (no truck on the lane) some interesting findings were obtained. When the normal traffic flow is disturbed by the presence of a truck, we find a small, but statistically significant—F(1,1074) = 22.830, p = .0001)— decrease in the vehicles speed. What is more interesting is the fact that such a decrease depends on the lane where the measure is taken. The reduction in speed, in other words, occurs only in the slow and fast lanes (and it is approximately of the same magnitude) while no apparent effect was obtained in the overtaking lane The interaction is highly significant from a statistical point of view

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(F(2,1074) = 6.35, p = .0018). In other words: when the drivers saw the truck on the emergency lane they reduced their speed, but only if they were driving on the first two lanes; the behavior of the drivers in the overtaking lane was unaffected by the presence of the truck. While there was not possible to ascertain a direct, general effect of the system status (on vs. off) on vehicle speed, some findings suggest that some subtler effects could be detected by looking at the interactions among the different conditions. More particularly, it could be useful to look, according to the questions mentioned in the preliminary section, for the differential effects of the warning distance and the flashing patterns. Figure 1 illustrates the interaction between warning distance and activation status. The 250m condition had a highly significant (F(2, 1062) = 7.43, p = .0006) effect on speed which is completely different from the effects deriving from the other (i.e., the 500m and 750m) conditions. In these latter cases we find a small reduction in speed when the system is activated while in the former there is an increase in the speed with Companion on. We can speculate about the fact that, probably, within the 250m warning distance the truck is easily visible and, therefore, the drivers could immediately figure out the reason why the system had been activated. With a longer warning, on the other hand, being uncertain about what constitutes the hazard they are alerted against, they tend to reduce their speed.

Figure 1: Interaction plot of the status x distance conditions.

Independent from the plausibility of this hypothesis, however, it is a fact that the warning distance constitutes a potentially significant aspect that has to be taken into account in devising the system operational policy.

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This conclusion is confirmed by another analysis that can be performed on the same data. Table 3 partitions speed means by warning distance and condition. Only the conditions when the system was operational (i.e. the Alert—Companion system on but no obstacles—and the Activated condition —system on with a truck was standing on the road) have been considered. Table 3: Speed Means partitioned by warning distance and condition.

250m 500m 750m Mean

Alert 115.7 113.9 110.8 113.4

Activated 111.4 110.2 111.0 110.8

Mean 113.5 112.0 110.9

It was found that the warning distance had a significant effect on the speed (F (2, 522) = 3.24, p=.0398). Moreover, the drivers in the Alert condition drove slightly faster in comparison with subjects in the Activated condition. The difference is small in magnitude but statistically significant (F (1, 522) = 9.72, p=0.0019). There is however an interesting interaction which approximates significance (F(2,522) = 2.76,p=0.0644) between these two factors. While the drivers in the Activated condition drove more or less at the same speed, those in the Alert condition were more sensitive to the warning distance effect. In particular it was found that, when no precise hazard or danger is perceived, the more the warning lasts, the more the subjects are leaning towards reducing their speed. Another series of analyses were conducted on the data of this experiment to establish the influence of different flashing patterns. Only the data collected when the system was on (i.e., during the Activated and Alert phases) were utilized. Two conditions were contrasted. In the first one Companion alerted the drivers through a stroboscopic funnel (or “whip”) effect obtained by rapidly switching the lights of consecutive posts. In the second condition an up-down effect was obtained by rapidly switching the two light units of the same post. A significant general influence of the pattern was obtained: while Companion was displaying the funnel effect the mean speed was 110.6 km/h in comparison with the 113.7 km/h of the up-down condition (F(1,528)= 11.91, p = .0006). Some interesting interactions emerged from the analysis. While there is only a small difference in the effect of the pattern for the fast and overtaking lanes, there is an important reduction in the speed of vehicles in the slow lane with Companion in the funnel condition (F (2,528) = 4.65, p = .01). This is quite surprising since the light posts were located in the center of the motorway and should therefore be less visible by people driving along the first lane. Figure 3 shows the effect of the flashing patterns in the different phases in which Companion was operational.

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Figure 3: The effect of flashing pattern in the different phases.

The figure confirms the stronger effect of the funnel vs. the up-down pattern. This effect is most beneficial during the Alert phase, when the system is on but no danger or hazard is apparently present on the road. This result can be explained by the fact that, as we have just seen, during the Activated phase the drivers tend to reduce spontaneously their speed since the danger they are warned against is visible. In the Alert phase, on the other hand, only the warning lights are perceived, and in this condition the two patterns play a different role in directly influencing the vehicle speed.

RESULTS OF EXPERIMENT 2 As a first analysis on the data of Experiment 2, a three-way ANOVA was carried out to assess the influence of the principal experimental factors (status of the system, message delivered through the VMS panel, lane in which the speed has been recorded) and their interactions. Statistically significant effects for the status and lane were found, while the kind of the message, as such, did not directly influence vehicle speed. When Companion was on, there was a decrement in speed of about 3 km/h in comparison with the system was off. The magnitude of the difference is small but the effect is highly significant from a statistical point of view (F(1, 4305) = 36.2 p = .0001). The other main effect is that of the lane (F(2, 4305) = 5161.1 p = .0001), which is hardly surprising. In comparison with those obtained in Experiment 1, present data show however a different pattern. There is now a huge difference (about 40 km/h) between the speeds of vehicles in the slow and fast lane. The difference between the fast and overtaking lanes (about 3 km/h), however, while still significant (at the level of p=.0001) is greatly reduced. This finding is explained by the fact that speed measurements were taken 200 meters before the closure of the overtaking lane: drivers are obviously forced to slow down and to switch to their right.

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Some interesting interactions emerged from the analysis. Under this experimental condition, the activation of Companion had absolutely no effect upon the vehicles in the slow lane, a small effect upon the vehicles in the fast lane and a greater influence for those travelling on the overtaking lane (F(2,4305) = 11.6, p = .0001). These results are assuring since they indicate that the system was more effective where its influence was mostly needed, i.e. in inducing the drivers in the most dangerous condition to reduce their speed. While the message on the VMS panel had no direct influence on the driving speed (the message was delivered approximately 10 km before the speed measures were taken), there is an interesting and significant interaction (F(1, 4305) = 10.1, p = .0015) of the message content with the status of the system. The interaction is shown in figure 4. The beneficial effect of the system activation is enhanced when a relevant message (alerting the drivers about the lane closure) is displayed on the VMS panel. While the magnitude of the effect with neutral messages is quite small (1 km/h), it becomes bigger (approximately 4 km/h) when the drivers have been warned about the lane closure.

Figure 4: The status x lane interaction plot.

This result is also promising, since it opens the possibility of a fruitful synergy between different road information and warning systems. A different set of analyses have been performed on the data collected when the system was activated in order to evaluate the possible effects of different warning distances. It was obtained that the distance is a critical factor (F(2,3219 = 6.28, p = .0019) in determining the efficacy of the system. Figure 5 illustrates the results.

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Figure 5: The effect of warning distances on vehicle speed.

The data support the hypothesis of the existence of an optimal interval within which the system is maximally effective. A warning of 250m is probably too small to produce some useful effect while a 750m warning could be perceived as lasting too long. A significant interaction (F(4, 3219) = 3.60, p= .0062) between warning distance and lane has been found. For the vehicles travelling on the slow lane, the warning distance plays absolutely no role: the differences between the means speeds are always less than half a km/h. The same thing can be said for the vehicles in the overtaking lane; in this case the biggest difference (between 750m and 500m) is about one km/h. The effect of the distance seems thus reserved to vehicles driving on the fast lane. No other significant interactions were found, in particular no differential effect of the message has been found on the role of different warning distances, which seems a sensible outcome. CONCLUSIONS In the first experiment, in which an incident to a truck was simulated, no main effect that could be ascribed to the activation of Companion was reported. In particular, no significant reduction in speed of the order of magnitude found in the previous investigations has been obtained. The main reason could be attributed to the different settings of the evaluation studies. A4 is a wide, spacious, three lanes (+ emergency) motorway with optimal visibility conditions. The perceived risk of a truck resting on the emergency lane was very small and the efficacy of the warning system greatly reduced. This negative result notwithstanding, some significant effects of the variables manipulated during the experiment were obtained. In particular, the role of the warning distance has been stressed. A critical factor seems to be whether the dangerous situation the drivers are alerted against is directly visible or not. Some suggestion has been obtained that, when no precise hazard or danger is perceived, the more the warning lasts, the more the subjects are leaning towards reducing their speed.

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Another interesting outcome of the first experiment concerns the role of the flashing pattern. Some unexpected results have been found. While a funnel effect was displayed, the system had the greatest influence on the vehicles travelling on the slow lane, i.e. the lane that is the farthest from the light posts but the one where the stroboscopic effect of the apparent movement is most visible. The results of the second experiment, in which Companion warned the drivers about a lane closure, suggest that it is important to take into account the scenario in which the system is utilized. When Companion was activated a small, but highly significant, reduction in the vehicles’ speed was obtained. The reduction was greatest for the vehicles travelling on the overtaking i.e., the system was more effective where its influence was mostly needed. In this experiment the interaction between warnings delivered by Companion and the VMS panels was also investigated. It was found that the effect of the system was enhanced when a relevant message (alerting the drivers about the lane closure) was displayed by the panels. This result is also promising, since it opens the possibility of a fruitful synergy between different information and warning systems. A further confirmation of the role of the warning distance was also obtained with data supporting the hypothesis of the existence of an optimal interval within which the system is maximally effective. Questionnaires and interviews administered to more than 400 drivers allowed to ascertain the general positive attitude toward Companion and the expectations people drivers have concerning the efficacy of the system in reducing accident risks and improving driving safety.

REFERENCES (1)

Klassen, N., Tarry, S. and Tognoni G. (1997) A new quality in roadside incident warning. Proceedings of the Fifth ITS World Congress, Berlin.

(2)

Klassen, N. (Ed.) (1998) Telematics applications in Bavaria, Scotland, and Others. Project number TR1054: Final Report.

(3)

Lerner, G., Huber, W, and Krause, G. (1997) COMPANION: Development and field testing of a collective warning system. Proceedings of the Fifth ITS World Congress, Berlin.

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