Safety Performance of Combinations of Traffic and Roadway Cross-Sectional Design Elements at Straight and Curved Segments
Publication: Journal of Transportation Engineering, Part A: Systems
Volume 143, Issue 6
Abstract
This study develops various crash modification factors (CMFs) for combinations of traffic and roadway cross-sectional elements at noncurved (i.e., straight) and curved roadway sections using the cross-sectional method. Generally, a CMF estimates the expected changes in crash frequency after a single specific treatment is implemented on a roadway. The results indicate that increasing lane width, increasing shoulder width, and their combination are safety effective in reducing crash frequency in general. In particular, it was found that crash frequency decreases as the lane width increases until 3.51 m (11.5 ft) width and it increases as the lane width exceeds 3.51 m. The crash rates start to decrease again after 3.81 m (12.5 ft). The results also indicate that the developed nonlinearizing link function derived nonlinear relationship between crash rates and lane width, and this relationship was clearly reflected in the generalized nonlinear models (GNMs). Moreover, there is a significant interaction impact between lane and shoulder widths at segments with a horizontal curve whereas the interaction term is not significant at noncurved segments. It was also found that the CMFs for increasing lane and shoulder widths are decreasing as annual average daily traffic (AADT) level increases. Based on the findings from this study, it is recommended to apply the proposed methodology of utilizing the GNMs with interaction terms in the cross-sectional method to (1) estimate more accurate CMFs for single treatments and combinations of treatments and (2) reflect the nonlinearity of crash predictors and interaction impacts among variables.
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Acknowledgments
The authors wish to thank the Florida Department of Transportation (FDOT) for providing the data that were used in this study, and for funding this research.
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Published In
Journal of Transportation Engineering, Part A: Systems
Volume 143 • Issue 6 • June 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: Apr 14, 2016
Accepted: Oct 26, 2016
Published online: Feb 17, 2017
Published in print: Jun 1, 2017
Discussion open until: Jul 17, 2017
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