Estimation of the Safety Effectiveness of Lane and Shoulder Width: Case-Control Approach
Publication: Journal of Transportation Engineering
Volume 133, Issue 6
Abstract
There is a need to better understand and quantify the safety implications of geometric improvements and countermeasures. A commonly accepted measure of safety effectiveness is the crash modification factor (CMF) defined as the expected number of crashes with a countermeasure divided by the number expected without the countermeasure. This paper evaluates the use of a case-control design to directly estimate the safety effectiveness of lane and shoulder width using the odds ratio: the probability of a crash with the countermeasure divided by the probability of a crash without a countermeasure. The case-control design is well established in epidemiology where it is used to relate risk factors within a study population to a particular outcome or disease. In the highway safety context, the “outcome” is defined as a crash, the “risk factor” is a particular geometric feature or countermeasure and the “subjects” are roadway segments. This paper describes the outcome of an experiment in which commonly available crash, roadway and traffic data are used to estimate odds ratios which are compared to CMFs from the literature. The comparison of these slightly different effectiveness measures are intended as a test of the efficacy of the case-control method in safety effectiveness evaluation. Geometric, traffic and crash data were obtained for more than 28,000 rural two-lane undivided highway segments in Pennsylvania for years 1997 to 2001 inclusive. A matched case-control design is developed to estimate the safety effectiveness of different lane and shoulder widths while adjusting for the confounding variables: speed limit, average daily traffic and segment length. Conditional logistic regression models are developed to estimate the odds ratio for lane and shoulder width separately. Lane and shoulder width odds ratios compare favorably to CMFs from the literature and have the additional advantage of including confidence intervals on the estimates. The paper concludes with a discussion of strengths and weaknesses of the method and recommendations for future research.
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References
Braver, E. R., Zador, P. L., Thum, D., Mitter, E. L., Baum, H. M., and Vilardo, F. J. (1997). “Tractor-trailer crashes in Indiana: A case-control study of the effect of truck configuration.” Accid. Anal Prev., 29(1), 79–96.
Collett, D. (2003). Modeling binary data, 2nd Ed., Chapman and Hall/CRC, New York.
Greenland, S., Robins, J. M., and Pearl, J. (1999). “Confounding and collapsibility in causal inference.” Stat. Sci., 14(1), 29–46.
Griffin, L. I., and Mak, K. K. (1987). “Benefits to be achieved from widening rural, two-lane, farm-to-market roads in Texas.” Transportation Research Board 67th Annual Meeting, Washington, D.C.
Harwood, D. W., Council, F. M., Hauer, E., Hughes, W. E., and Vogt, A. (2000). “Prediction of the expected safety performance of rural two-lane highways.” FHWA-RD-99–207, Federal Highway Administration, Washington, D.C.
Hauer, E. (1997). Observational before-after studies in traffic safety, Pergamon, New York.
Hauer, E. (2000). “Truck safety: A chronological reading of the literature.” ⟨http://roadsafetyresearch.com⟩ (Aug. 22, 2006).
Híjar, M., Carrillo, C., Flores, M., Anaya, R., and Lopez, V. (2000). “Risk factors in highway traffic accidents: A case-control study.” Accid. Anal Prev., 32(5), 703–709.
Jovanis, P. P., and Chang, H. (1989). “Disaggregate model of highway accident occurrence using survival theory.” Accid. Anal Prev., 21(5), 445–458.
Jovanis, P. P., Park, S. W., Chen, K. Y., and Gross, F. (2005). “On the relationship of crash risk and driver hours of service.” 2005 Int. Truck and Bus Safety and Security Symp., National Safety Council, Alexandria, Va.
Schlesselman, J. J. (1982). Case-control studies: Design, conduct, analysis, Oxford University Press, New York.
Shen, J., and Gan, A. (2003). “Development of crash reduction factors: Methods, problems, and research needs.” Transportation Research Record. 1840, Transportation Research Board, Washington, D.C., 50–56.
Stein, H. S., and Jones, I. S. (1988). “Crash involvement of large trucks by configuration: a case-control study.” Am. J. Public Health, 78(5), 491–98.
Stevenson, M. R., Jamrozik, K. D., and Spittle, J. (1995). “A case-control study of traffic risk factors and child pedestrian injury.” Int. J. Epidemiol., 24(5), 957–964.
Tsai, Y. J., Wang, J. D., and Huang, W. F. (1995). “Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.” Int. J. Epidemiol., 142(9), 974–981.
U.S. Department of Transportation (USDOT). (2005). Traffic safety facts 2005: Motor vehicle traffic crashes as a leading cause of death in the United States, National Center for Statistics and Analysis, Washington, D.C.
Woodward, M. (2005). Epidemiology: Study design and data analysis, 2nd Ed., Chapman and Hall/CRC, New York.
Zegeer, C. V., Deen, R. C., and Mayes, J. G. (1981). “Effect of lane and shoulder widths on accident reduction on rural, two-lane roads.” Transportation Research Record. 806, Transportation Research Board, Washington, D.C., 33–42.
Zegeer, C. V., Hummer, J., Reinfurt, D., Herf, L., and Hunter, W. (1988). “Safety effects of cross-section design for two-lane roads.” Transportation Research Record. 1195, Transportation Research Board, Washington, D.C., 20–32.
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© 2007 ASCE.
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Received: Mar 21, 2006
Accepted: Dec 14, 2006
Published online: Jun 1, 2007
Published in print: Jun 2007
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