U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
|Publication Number: FHWA-HRT-13-044 Date: August 2013|
Publication Number: FHWA-HRT-13-044
Date: August 2013
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This report may be of use to traffic engineers and researchers who are concerned with the conspicuity of traffic signs.
The Manual on Uniform Traffic Control Devices advises that, “Signs should be placed on the right side of the roadway where they are easily recognized and understood by road users.” Guidance is provided on the spacing and prioritization of signs, and in some conditions, additional steps may be needed to ensure that signs are conspicuous. Engineering judgment is required when locating signs. However, little additional information is available to engineers to assist in making such judgments. The research described in this report was intended to develop scientific support for additional guidance on traffic control device conspicuity. The report concludes with guidance on sign conspicuity enhancement for practitioners and provides suggestions for additional research to advance the overall state of knowledge on sign conspicuity.
Monique R. Evans
Director, Office of Safety
Research and Development
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.
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Technical Report Documentation Page
|1. Report No.
|2. Government Accession No.
|3. Recipient's Catalog No.
|4. Title and Subtitle
Traffic Control Device Conspicuity
|5. Report Date
|6. Performing Organization Code|
Vaughan W. Inman, Stacy A. Balk, William A. Perez
|8. Performing Organization Report No.|
|9. Performing Organization Name and Address
6300 Georgetown Pike
McLean, VA 22101-2296
|10. Work Unit No. (TRAIS)|
|11. Contract or Grant No.
|12. Sponsoring Agency Name and Address
Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, DC 20590-9898
|13. Type of Report and Period Covered
Final Report. 10/1/2008-9/30/2011
14. Sponsoring Agency Code
|15. Supplementary Notes
FHWA Contracting Officer's Technical Representative (COTR) was Chris Monk (HRDS-30).
The conspicuity of a traffic control device (TCD) is defined as the probability that the device will be noticed. However, there is no agreed-upon measure of what constitutes being noticed. Various measures have been suggested, including eye fixations, recall, and verbal reports. Four conspicuity studies are discussed in this report.
It has been observed that conspicuity is not solely a property of a TCD but must include consideration of the surrounding environment. The first of the studies described in this report used multidimensional scaling (MDS) to identify factors that characterize drivers' perceptions of TCD environments. The MDS study revealed that two dimensions, clutter and predictability, characterized the roadway environments included in the study.
In the second study, drivers' eye glances to TCDs were recorded on a 34-mi (55-km) drive. After passing selected TCDs, drivers' recall of the TCD was assessed by asking them to identify it. That study showed that warning signs are seldom glanced at and only about half of them are recalled just 2 s after they are passed. About 20 percent of speed limit signs received glances, but drivers were aware of the posted speed limit about 80 percent of the time.
The third study examined drivers' ability to detect speed limit and warning signs. The ability to detect speed limit signs, as measured by conspicuity angle, was degraded by cluttered backgrounds. However, the detectability of fluorescent yellow-green warning signs was not affected by background clutter.
The fourth study examined the effect of background environment on drivers' ability to read TCDs. Background had no effect on speed limit sign readability and had a small effect on warning sign readability. Recommendations for enhancing the conspicuity of regulatory signs are proposed.
|17. Key Words
Conspicuity, Speed-limit sign, Warning sign, Sign detection, Sign recall, Eye tracking
|18. Distribution Statement
No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.
|19. Security Classification (of this report)
|20. Security Classification (of this page)
|21. No. of Pages
|Form DOT F 1700.7||Reproduction of completed page authorized|
Table 1. MDS coordinates of a two-dimensional solution for the panorama similarity ratings
Table 2. Matrix of correlations between each descriptor rating and each MDS dimension
Table 3. Percent fixated on and recalled for selected objects in Luoma study
Table 4. Percent correct recall of signs from Johansson and Backlund
Table 5. TCDs for which recall was requested and glances were tabulated
Table 6. Percent of TCDs of each type correctly and incorrectly identified as a function of whether drivers looked at them
Table 7. Identification responses to the slippery when wet warning sign
Table 8. Example critical detection conspicuity angle computation for one participant
|FHWA||Federal Highway Administration|
|GEE||Generalized estimating equations|
|MUTCD||Manual on Uniform Traffic Control Devices|
|ROI||Region of interest|
Traffic control device