Determining Colors for Traffic Control Devices at Transponder ...

Determining Colors for Traffic Control Devices at Transponder-Controlled Tollbooth Lanes with a Sign Simulator Gary A. Golembiewski, Bryan J. Katz, Richard L. Knoblauch, and Gabriel K. Rousseau and plazas because different payment options have become available to drivers. These typically lead to lanes for

The number of toll roads is increasing in the United States, and drivers face signing practices that vary greatly across jurisdictions. In addition to the increase in toll roads, there is an increase in the use of electronic toll collection (ETC) transponders. The present study was undertaken to develop standard signing practices—specifically for background color, legend color, underlay color (i.e., the background color for the pictographs), and pictograph—for ETC-supported toll road signs. The study reviewed selected ETC toll road signs in the United States to help select candidate elements and options to be used in a laboratory experiment. On the basis of that review, 120 signs depicted on 35-mm slides were developed with a standard sign-design software package. The signs were presented to 60 participants (equally divided by sex and age group) in the recently updated Turner–Fairbank Highway Research Center’s sign simulator. The signs were shown to participants starting at a simulated distance of approximately 1,125 ft (343 m), and then the image was zoomed toward the participants at a constant speed controlled by the laboratory’s computer. Each participant’s detection distance, guidance legibility distance, and pictograph legibility distance were recorded. The results showed that, overall, green as a background color obtained the longest guidance information legibility distance. Also, fonts that provided the highest contrast to the background color (such as white on black) were the most effective for legibility. Underlay colors that showed the highest contrast to the pictographs were the most effective and included all of the lighter colors tested (white, yellow, and blue).

1. Exact change, 2. Full service, and 3. Transponder-equipped vehicles only. Inadequate or inconsistent signing can lead to an increase in driver confusion and maneuver errors. Drivers trying to identify which lanes (sometimes among a total of 12 lanes) are ETC lanes, exact change, or full-service lanes have been observed (2). The informationprocessing demands at toll plazas, coupled with various driving speeds and frequent lane changing, highlight the need to improve signing on toll roads. Some states, such as those in the Northeast Corridor, are providing systems such as E-ZPass, which offer an interstate, integrated payment option for tolls. This system allows drivers to travel on major freeways with a single transponder that works on all toll systems in each of the cooperating states. Although a standardized toll road payment system is a boon to travelers, there is no standardized toll road signing system across the United States. The E-ZPass signs are relatively consistent in the different states where they are in operation. With slight variations, the pictograph’s color and font have become relatively standardized in the states that support this system. However, this situation is not universal; a number of neighboring states that offer ETC (including those with E-ZPass) have signs that are distinctly different from each other and reflect inconsistent applications. These practices can lead local drivers, who may have become accustomed to their native tollway sign and pictograph, to become confused when they travel to another state and who are faced with a new sign or pictograph for a different toll payment system. Adding to the confusion is the uncertainty of whether a neighboring state’s ETC lanes accept the driver’s transponder as payment.

The number of toll lanes and toll roads being developed is increasing and is expected to increase even more in the next decade (1). This issue is becoming more important because of recent increases in the design, construction, and operation of toll roads within the United States. In addition, new federal legislation has supported this trend by authorizing states to convert existing freeways to tollways (P.L. 105-178, Transportation Equity Act for the 21st Century, 1998). Already, 18 states have deployed electronic toll collection (ETC) transponders that support 3,505 toll lanes (1). Although those ETC-controlled toll lanes show significant increases in traffic flow, the increase in ETC facilities has led to more confusion at tollbooths

PROJECT OVERVIEW This study was conducted to develop a set of basic signing recommendations that can be consistently applied to toll roads that use ETC and that can be used to help develop design guidelines for additional elements of toll roads, such as pavement markings, variable message signs, and even radio broadcasts, to provide a consistent and comprehensive set of positive guidance information sources well in advance of a toll plaza. The results of this research can be used to provide traffic engineers with parameters such as the most effective distances of design elements and signs and the message

G. A. Golembiewski, Center for Applied Research, 2607 Soapstone Drive, Reston, VA 20191. B. J. Katz, Science Applications International Corporation, 6300 Georgetown Pike, F-215, McLean, VA 22101. R. L. Knoblauch, Center for Applied Research, 9661 Fringe Tree Road, Great Falls, VA 22066. G. K. Rousseau, FHWA, 6300 Georgetown Pike, T-210, McLean, VA 22101. Transportation Research Record: Journal of the Transportation Research Board, No. 1973, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 48–54.

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Golembiewski, Katz, Knoblauch, and Rousseau

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contents of signs that need to be conveyed to drivers. By integrating information from the various design elements, drivers could receive information from a number of different media so that they can plan correct lane placement as they near the toll plaza. The objective of the project was to develop a set of basic signing recommendations to be used by toll road designers and engineers to assist drivers in identifying those toll lanes designed for transponderequipped vehicles or ETC. The recommendations were based on an evaluation process that addressed background color, legend color, and overlay color in combination with pictographs displaying the various toll road sign names used at existing toll facilities.

RESEARCH METHOD State-of-Practice Survey To help determine which sign parameters would be included in the laboratory experiment, information was gathered from a number of toll roads and toll authorities in the United States. The toll roads chosen for the study included the Garden State Parkway (New Jersey), New Jersey Turnpike, Dulles Airport Toll Road (Virginia), Dulles Greenway Toll Road (Virginia), Harris County Toll Road (Texas), Hilton Head Island Tollway (South Carolina), New York Thruway, and West Virginia Turnpike. Toll road representatives were contacted and asked to supply information regarding the current signing practices on their roads. Information was gathered from telephone interviews, web searches, and materials received from toll road representatives. Sample signs as well as descriptions of the toll roads, drawings of the signs and their placement, and operational information were gathered. The collected information yielded a number of general findings that were considered for inclusion as parameters in the laboratory experiments. First, the toll road signs to be simulated would be based on an approach sign measuring 10 by 16 ft (3.05 by 4.88 m). Second, the letter height was set at 12 in. (305 mm), which exceeds the minimum recommendation in the Manual on Uniform Traffic Control Devices (MUTCD) of 10-in. (254-mm) letters for guidance information (3). Third, the approach speed for the simulation would be programmed at 35 mph (56 km/h). Finally, the pictographs represented on the signs were chosen to be FasTrak, E-ZPass, I-Pass, and EZ-TAG.

FIGURE 2 Sample sign stimuli (refer to Table 1 for color combinations tested).

of the Pooled Fund Study on Traffic Control Devices (TCD). Figure 1 illustrates the components found in each sign, and Figure 2 illustrates a sample of the signs used as part of the experiment.

Colors Discussions about the sign background color, legend color, pictograph color, and the color used under the logo (the underlay color) were undertaken to determine those colors most likely to be implemented by states, colors that were still unassigned, and other factors (Table 1). Background Color MUTCD currently designates white, green, yellow, and fluorescent pink for informational, guidance, warning, and incident management signs, respectively. Unassigned colors are available for other signs: blue, coral, and purple. A number of states have reported the use of fluorescent pink signs for incident management and traffic warnings. The following six colors were selected as appropriate for this study: black, white, yellow, green, blue, and purple.

Sign Stimuli Again, discussions with the TCD Pooled Fund Study members and the study team were conducted to select the legend colors and fonts that could be implementable. It was determined that the following legend colors would be included in the experiment: black, white, yellow, and green. The font would use FHWA Standard Highway Series D. Legend Color and Font

The sign stimuli used for the experiment consisted of 35-mm slides, presented to participants in the Turner–Fairbank Highway Research Center (TFHRC) sign simulator (SIGNSIM). The sign parameters and design were based on the field review information as well as a review of current toll road operations and discussions with members

Pictograph Guidance Information

Background Color

FIGURE 1

Example laboratory experiment sign.

Underlay Color

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Transportation Research Record 1973

TABLE 1

Sign Stimuli Color Parameters: Background Color, Legend Color, and Underlay Color

Background Color

Legend Colors

Underlay Colors

White Black Green Yellow Blue Purple

White, Black, Yellow, Green White, Black, Yellow, Green White, Black, Yellow, Green White, Black, Yellow, Green White, Black, Yellow, Green White, Black, Yellow, Green

Black, Green, Yellow, Blue, Purple White, Green, Yellow, Blue, Purple Black, White, Yellow, Blue, Purple Black, Green, White, Blue, Purple Black, Green, Yellow, White, Purple Black, Green, Yellow, Blue, White

Pictograph and Pictograph Color As discussed in the introduction to this report, the E-ZPass system is used by the majority of ETC lane operations and for the majority of ETC vehicle transactions in the country. E-ZPass systems are operational in New York, New Jersey, Pennsylvania, Maryland, Delaware, Massachusetts, West Virginia, and recently, Virginia; fully 35% of all ETC-supported toll lanes in the United States use the E-ZPass system. Similarly, this system (and color) is supported by approximately 40% of the agencies that oversee ETC-supported lanes. In addition, as new toll roads have opened in the eastern United States, they have built E-ZPass compatibility into their systems. They have also adopted the E-ZPass pictograph and color for their toll road signage. Because it appears that E-ZPass’s sign characteristics define the pictograph standard, it was decided that purple would be the only color for the pictograph. In addition, for the purposes of the experiment, toll road pictographs that comprised random letters were also included. These nonsense toll road pictographs were used in the experiment to help validate participants’ recognition and comprehension of the pictographs. By including nonsense letters, even though they are roughly designed like the real pictographs, it helped to keep the participants from guessing which pictograph they were viewing from a distance. Underlay Color Toll roads use different colors for the layer under-

neath the pictograph. For this experiment, this was termed the “underlay.” As with the background sign parameters, it was decided that all background sign colors should also be used for the underlay. The final experimental design included six background colors, four legend colors, and five underlay colors. The combination of all factors resulted in 120 signs representing all combinations. All combinations were used in the experiment, including those combinations in which the color of the font was identical to the background color, for example, the black font on the black background. Essentially, this condition resulted in a sign with a blank lane assignment field. A blank lane assignment field was used, as with the random toll road names, to help provide a check of the validity of the participants’ responses and whether they were providing guesses about the guidance information, especially for those signs with font and background colors with low contrast, such as a yellow font on a white background.

Sign Production The slides were created with SignCAD, a sign-making application that highway engineers typically use to design signs for state departments of transportation. The font used was Series D of the Standard Highway Alphabet. All colors used met the requirements of 23 CFR, Part 655 Appendix, for the use of colors on highway traffic signs. All signs were produced digitally and were converted to 35-mm slides for use in the TFHRC SIGNSIM. Research Participants Sixty participants were included in the experiment, and the group was equally divided by sex. Participants ranged in age from 19 to 89 years and were grouped into two equal age groups: younger (under 60 years of age) and older (60 years of age and over). This resulted in 15 participants in each age group–sex combination. The participants were volunteers recruited from the subject pool list maintained by the Human Centered Systems Team at TFHRC and were primarily from the Northern Virginia area. All participants were licensed drivers, and each participant received $30 when he or she completed the experiment. The average age for the young drivers was 38.4 years and was roughly equivalent for both the men and women. The men and women in the older group, with an overall average age of 72.7 years, had almost identical mean ages. An information sheet that the participants completed at the conclusion of the experiment provided information on their current driving habits on freeways and toll roads. When the results were broken down by sex, age, and age by sex, they showed essentially no difference in the volunteers’ driving experiences. Only a few participants (8.5%) reported that they owned transponders for the Northern Virginia toll roads (Dulles Toll Road and Dulles Greenway). Although they reported that they traveled on the area and regional toll roads on an infrequent basis, they were aware that lanes were dedicated for ETC use. Their experience reflected correct lane choice and use and did not have an impact on their understanding or perception of the signs. Experimental Apparatus

Guidance Information In addition to the pictographs, the sign included informational and lane assignment information to guide drivers to the correct ETC lanes. All signs included the message “Toll Plaza 1 Mile” or “Pay Toll 1 Mile.” In addition, the signs included one of four lane assignment messages that were randomized across the 120 signs and included “2 Left Lanes,” “2 Right Lanes,” “Left Lane,” and “Right Lane.”

The experiment was conducted in the recently updated SIGNSIM at TFHRC. This laboratory is used to present specific stimuli to participants in a highly controlled environment. The experiment used a computer-controlled slide projector that displayed the signs with a zoom lens that gradually increases the sign size to simulate driving at 35 mph. Additionally, SIGNSIM was updated to also use a lightfiltering wheel to make sure that the participants saw a constant light


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level as the signs were enlarged. A computer that used National Instruments LABVIEW software and hardware controlled the zoom lens, light filter, and slide selection. The slides are shown on a rearprojection screen. The participants viewed the images from the front of the room. The overall relationship used to determine the distance to a simulated sign is based on the concept of similar triangles, as shown in Figure 3. The actual height is the stated height of the simulated sign, whereas the presentation height is the measured dimension of the projected sign on the SIGNSIM screen. The viewing distance is the distance between the participant and the SIGNSIM screen. By using these known values, the actual distance at which an actual sign would be detected or become legible can be calculated. The similar triangles produced in the figure gives the relationship for determining the actual distance of the sign as

Experimental Procedure The participants began the experiment seated 12.5 ft (3.81 m) from the rear-projection screen in SIGNSIM. The experimenter explained to them that the study was being conducted to help FHWA design signs and that they were to look at the signs as shown on the screen and press the response button three different times to provide three different responses: 1. The first response indicated when they first saw the sign on the screen (detection). 2. The second response indicated when they decided that they could correctly read the guidance information (lane assignment) on the sign (guidance legibility) and then read it aloud. 3. The third response indicated when they decided that they could correctly identify the pictograph on the sign (pictograph legibility) and then read it aloud.

viewing distance presentation height = actual distance actual height

Each participant was presented 60 slides, one-half of the total of 120 signs. Each set of slides was randomly assigned to the participants, and the order of presentation was randomized to control for color combination and order effects. The experiment began when the participant had completed a series of practice slides and felt comfortable with the experimental procedures. The servomotor input voltage was recorded on the computer for each of the responses, and the experimenter recorded if the participant’s reading of the information was correct. After the recording of the first and the second responses, the screen would darken for 2 to 4 s, and the sign would be displayed again and zoom toward the subject, starting from the point at which it had stopped. At that time the participants would press the button when they determined that they could read the sign. After the third response was recorded, the screen would darken for 2 to 4 s and the next sign was presented. After all 60 signs were presented, the participants were debriefed and given a short information sheet to complete. The information sheet requested information related to the participants’ driving experience, experience driving on toll roads and highways, and experience with ETC.

which can be converted to actual distance =

viewing distance × actual height presentation height

The next step was to determine the presentation height of the sign on the screen, given various voltage readings from the SIGNSIM controller. The SIGNSIM zoom function for varying the presentation height of the simulated sign worked by varying the voltage to a servomotor, which controlled the zoom lens. By comparing the input voltages with the resultant presentation height, the input voltage could be used to determine the actual distance. The following fourth-order regression, with an R2 value of .9995, was found for the computation of the actual distance from the input voltage: actual distance = 4.796 ( voltage 4 ) − 48.192 ( voltage 3 ) + 212.65 ( voltage 2 ) − 273.09 ( voltage ) + 432.43

RESULTS The participants pressed a response button to mark the following three separate events, which were recorded as distances:

Detection Distance

1. Initial detection of the sign, 2. Legibility of the guidance information, and 3. Legibility of the pictograph.

Detection distance was defined as that point at which the participants were able to detect a sign on the screen. As Figure 4 illustrates, this distance averaged over 1,000 ft. This result can also be seen as

Simulated Distance

Simulated Height

Actual Distance

FIGURE 3

Depiction of relationship of simulated size to actual sign size.

Actual Height

Distance (feet)

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1200

TABLE 3

1000

Font Color

Summary of Legend Color Across All Background Colors Mean Legibility Distance

Standard Deviation

410 420 417 398

152 137 136 160

Black Green White Yellow

800 600 400 200 0 Black

FIGURE 4

Green

White Yellow Light Blue Purple Background Color

Overall sign detection distance.

the baseline for the next two legibility measures. This distance reflects the point when the participants could first detect the sign, not recognize or read it. An analysis of variance revealed no significant differences among the background colors for detection distance (F = 1.37, p < .09). Of course, signs do not consist only of a background color; and a sign’s effectiveness is a result of the other elements, such as the legend color. Therefore, the analysis proceeded with an assessment of the background and the legend colors in combination.

Legibility Distance

Guidance Information For legibility distance, multiple pairwise comparisons were conducted and yielded the following results: for background color, F(1,5) = 25.22 and p < .0001; for font, F(1,3) = 9.46 and p < .0001; and for background and font, F(5,3) = 32.94 and p < .0001. Table 2 summarizes the distances (in feet) obtained for background color, legend color, and the combination of background color and legend color. No differences were found by the lane assignment message (i.e., “2 Left Lanes,” “2 Right Lanes,” “Right Lane,” and “Left Lane”). The participants were able to read each of the messages equally well. As shown in Table 2, signs with a green background were read from the longest distance, followed by black, white, and yellow. When the legend alone is considered (Table 3, in which the distances are in feet), the legibilities of the guidance information when white and green legends were used were essentially equal, followed by the legibilities of black and yellow. Table 4 depicts the effect of the contrast between the background and the legend colors. As shown in Table 4, those sign combinations with the highest contrast

TABLE 2

Pictographs When the legibility distance for the identification of the pictographs is considered, the pictograph design, underlay color, and sign background color were assessed. These elements were seen as the most critical factors for alerting drivers, especially nonlocal individuals, as they approached a toll plaza and ETC lanes. It is important to remember that all pictographs in this experiment were purple; therefore, the only factor under consideration for this element was the design. TABLE 4 Summary of Background by Legend Color with Respect to Legibility Distance Guidance Information

Summary of Background Color Across All Legend Colors

Background Color Black Green White Yellow Light blue Purple

between the legend and the background were legible from the farthest distance. Of interest is the fact that the combination of a yellow legend and a green background was legible from the greatest distance, although signs consistent with the current practices of a white legend on a green background had essentially the same legibility distance. Nonstandard combinations of white on purple, blue on black, and purple on yellow also obtained long legibility distances, reinforcing the impact of high contrast on legibility. Figure 5, which compares the legibility distances of all combinations of background and legend colors, supports the design guidelines for the use of a high contrast between the background and the legend. Those signs with the highest contrast obtained legibility distances significantly greater than those with low contrast. These findings reinforce the current design convention of a white legend on a green background. Also of interest is the fact that a comparison by age showed that older participants’ responses showed a significantly shorter legibility distance [t(1) = 88.6, p < .0001]. The overall difference between the older and the younger groups was approximately 10%. The older participants were able to read the signs at an average of 461 ft, whereas the average for the younger participants was 515 ft. These results were relatively constant over all background and legend colors. This finding is consistent with those of other studies and might indicate that older drivers could benefit from more frequent signage to ensure that they are guided to the correct lanes farther downstream. This recommendation would probably help all drivers.

Mean Legibility Distance

Standard Deviation

438 456 405 399 384 398

138 148 136 129 160 148

Distance by Font Color (ft) Background Color

Black

Green

White

Yellow

422

437 474

457 486 344

Black Green White Yellow Light blue

415 435 430 462

438 426 444

342 368

262

Purple

310

373

467

443


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600

Distance (feet)

500 Overall Mean

400 300 Black 200

White

100

Green Yellow

0 Black

Green

White Yellow Light Blue Background Color

Purple

FIGURE 5 Legibility distance: comparison of all combinations of background and legend colors.

Analysis of these variables found that all of them were significant factors in relation to the legibility distance. t-tests of the data yielded the following results: for background color, t(5) = 23.42 and p < .0001; for underlay color, t(5) = 37.36 and p < .0001; and for pictograph, t(5) = 87.44 and p < .0001. Tables 5 through 8 summarize the legibility distances (in feet) for the different background colors, underlay colors, and pictographs. As shown in Tables 5 through 8, the green background color yielded the farthest legibility distance measurements, similar to the results of the guidance information. This lends support to the current common practice of using green as the background color. However, signs with dark colors for the background, such as purple and black, also fared well. Because of the dark (purple) color of the pictograph, the underlay colors shown to be the most effective were those that were lighter and that had a high contrast to purple. The most effective were white, blue, and yellow. Conversely, signs with black and green underlays had significantly shorter legibility distances. Purple was not included in this analysis, as a purple underlay with a purple pictograph would be viewed as a blank purple field.

TABLE 5

Pictograph Legibility Distance by Background Color

Background Color Black Green White Yellow Blue Purple

TABLE 6

Standard Deviation

188 217 166 183 178 194

88 112 105 90 99 99

Pictograph Legibility Distance by Underlay Color

Underlay Color Black Green White Yellow Blue

Mean Legibility

Mean Legibility

Standard Deviation

159 165 213 203 210

99 81 101 102 107

Finally, as shown in Table 8, the participants were able to read the EZ-TAG pictograph at a much longer distance than any of the other alternatives. This finding may be due to the relative simplicity of the design, since it is just text, as well as to the relatively high ratio of the pictograph to the underlay color. The EZ-TAG pictograph has relatively more empty space that helps to separate the figure from the background (i.e., the pictograph from its underlay color). The designs of E-ZPass and I-Pass are more stylized and appear to take longer to process. Similarly, the FasTrak logo also contains more design elements. Focusing on the underlay–pictograph combinations, Table 8 summarizes the legibility distances for each. Figure 6 shows the relationships between the two elements. The distances for the EZ-TAG pictograph were greater than those for any other pictograph, even when the distances are compared across all underlay colors. This was especially apparent for the lighter colors (with greater contrast), such as blue, yellow, and white. In fact, a blue underlay paired with the purple pictograph yielded legibility distances between 40% and over 100% better than those for the other pictographs. Also of note is the relatively high legibility distance of

TABLE 7

Pictograph Legibility Distance by Pictograph

Pictograph EZ TAG E-ZPass FasTrak I-Pass

Mean Legibility

Standard Deviation

268 178 157 193

117 98 72 92

TABLE 8 Pictograph Legibility Distance by Pictograph and Underlay Color Underlay Color Pictograph EZ TAG E-ZPass FasTrak I-Pass

Black

Green

White

Yellow

Blue

202 137 124 150

210 158 146 186

282 216 188 188

295 199 176 193

326 175 162 202

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350

EZ TAG E-ZPASS FasTrak I-PASS

Distance (feet)

300 250 200 150 100 50 0 Black

Green

White Yellow Underlay Color

Blue

FIGURE 6 Pictograph legibility distance: summary of all pictographs by underlay color.

EZ-TAG even with a black (low-contrast) background color. Figure 6 depicts the legibility distances for all the combinations of pictographs and underlay colors and demonstrates the significantly longer distances obtained with the EZ-TAG pictograph. This generally supports the view that simpler is better when the designs to be used on toll roads are considered. In addition, similar to the findings of the analysis of the legibility distances for different background colors and legend colors, significant differences were also found for the pictograph legibility distance between the older and the younger participants [t(1) = 84.6, p < .0001]. The magnitude of the difference was even more striking, with a difference of almost 20% between the overall legibility distances (across all underlay colors and pictographs). These differences were most apparent with the E-ZPass, I-Pass, and FasTrak pictographs, although the difference was still evident with the EZ-TAG pictograph.

read from a significantly farther distance than the other pictographs tested (E-ZPass, I-Pass, and FasTrak). This was interpreted to be due to its relative simplicity and the ratio of the size of the figure to its background, especially compared with the readability with light underlay colors (although this pictograph performed much better with all underlay colors). Finally, consistent with other research involving older drivers, the older participants had significantly shorter legibility distances (although not detection distances) than their younger counterparts. Overall, the differences ranged from approximately 10% for the guidance information legibility distance to approximately 20% for the pictograph legibility distance. The differences were consistent across combinations of colors and elements. On the basis of these results, the following recommendations are offered: • Green is the established guidance sign color. Its effectiveness in this study shows that it should be retained and that the legend color should remain white. • Purple as the pictograph color appears to be a good choice, but only if its underlay is a highly contrasting color, such as white, green, or blue. • This study shows that there is some evidence that more stylized pictographs can be difficult to read, especially at farther distances and for drivers who may be new to the toll facility. It is recommended that to help drivers read pictographs, the type of design should be carefully considered. • Finally, the findings support the findings of other research showing that older drivers need more time to perceive and process information. This should be considered for guidelines on sign placement and frequency along toll roads. The research results from this project may be useful in a larger effort to develop consistency across all ETC facilities, as such facilities have many geometric configurations, toll lane assignments (right, varied, or left), and other characteristics that differ.

CONCLUSIONS AND RECOMMENDATIONS This study was conducted to help determine the general design guidelines to be used when the signage on toll roads that support ETC is considered. Six different background colors were used in combination with four legend colors and four toll road ETC pictographs currently in use. The study also showed that an interactive sign simulator is useful for determining the relative detection and recognition distances between signs with various characteristics, such as different colors, symbols, legends, as well as sizes. It is recommended that a future study perform a field validation of the distances determined in the SIGNSIM compared with the actual distances determined in the field. However, for this study, relative distances are adequate for the comparison of one sign with another. Consistent with current guidance signing practices, the green background sign with a white font was shown to have significantly longer legibility distances for the guidance information. Other combinations that also showed high contrast, such as purple and black backgrounds with white or yellow fonts, also had long legibility distances; but when current practices and guidelines are considered, they would not warrant implementation. Similar to the findings for the different background and legend color combinations, the color that is under the toll road pictograph (underlay) and the pictograph design also appear to affect the legibility distance significantly. The subjects’ responses to the different pictograph designs showed that the EZ-TAG pictograph could be

ACKNOWLEDGMENTS The authors thank Joe Moyer, the contract officer’s technical representative for the project, and the members of the Traffic Control Devices Pooled Fund Study, especially Scott Wainwright, for their insights into the issues of ETC signing and their comments and contributions to the experimental plan. Lavonne Warder of the Center for Applied Research was instrumental in scheduling the participants and conducting the experiment. The authors also thank Steve Fleger and Dana Duke of Science Applications International Corporation, who were instrumental in implementing the software applications and data collection procedures for the laboratory experiment. REFERENCES 1. Metropolitan Summary of Toll Collection Lanes with Electronic Toll Collection (ETC) Capability. ITS/Joint Program Office, U.S. Department of Transportation. Revised 2003. www.itsdeployment.its.dot.gov/ results.asp?id=450&rpt=m&filter=1. 2. Chao, X. Design and Evaluation of Toll Plaza Systems. Department of Industrial and Manufacturing Engineering, New Jersey Institute of Technology, 2002. 3. National Standards for Traffic Control Devices: The Manual on Uniform Traffic Control Devices for Streets and Highways, Revision 1. FHWA, U.S. Department of Transportation, 2003. The Traffic Control Devices Committee sponsored publication of this paper.