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Accession Number PB2013-102369
Title Potential Safety Effects of Lane Width and Shoulder Width on Two-Lane Rural State Highways In Idaho.
Publication Date Jul 2012
Media Count 52p
Personal Author A. Abdel-Rahim J. Sonnen
Abstract This study provides a comprehensive evaluation of the relationship between crash rates and shoulder width and lane width for two-lane rural state highways in Idaho. Crash Modification Factors (CMFs) for shoulder width and lane width were developed using Idaho crash data covering the period from 1993 to 2010. The CMFs developed as part of this project will allow ITD to assess the potential safety benefits of shoulder widening projects. In addition to all crashes, models for single-vehicle and multiple-vehicle crashes were also developed. The CMFs presented in this study follow the general trends of prior knowledge and research. The results of the analysis showed that there is no significant difference between 12 ft lanes and 11 ft lanes in terms of safety for all types of crashes. The CMF for highways with 11 ft lanes was 1.02 indicating a marginal 2 percent increase in all crashes in comparison to highways with standard 12 ft lanes. The CMFs for highways with very small shoulders (less than 1 ft) were 1.16, 1.17, and 1.15 for all crashes, single-vehicle crashes, and multiple-vehicle crashes, respectively. This corresponds to an average increase in crashes of 16 percent when compared to highways with a 3-ft shoulder width. For highway sections with a shoulder width of 8 ft or more, the CMFs were 0.87, 0.90, and 0.83 for all crashes, single-vehicle crashes, and multiple-vehicle crashes, respectively, indicating an average reduction in crashes of approximately 13 percent when compared to highways with a 3-ft shoulder width. Idaho's crash data was also used to investigate the characteristics of pedestrian and bicycle crashes on two-lane rural highways. The results show that roadway sections with a right paved shoulder width of 4 ft to 6 ft had the lowest number of pedestrian and bicycle crashes. The probability for a pedestrian/bicycle crash increases significantly for roadway sections with shoulder widths less than 3 ft. The likelihood of a crash also increases for roadway sections with shoulder widths of 8 ft or more.
Keywords Accident analysis
Accident reduction
Crash Modification Factors (CMFs)
Highway Safety Improvement Program
Lane roads
Lane width
Motor vehicle crashes
Rural areas
Shoulder width
State transportation department
Traffic safety
Two lane roads

Source Agency Federal Highway Administration
NTIS Subject Category 85D - Transportation Safety
85H - Road Transportation
43G - Transportation
91B - Transportation & Traffic Planning
Corporate Author Idaho Univ., Moscow. National Inst. for Advanced Transportation Technology.
Document Type Technical report
Title Note Final rept.
NTIS Issue Number 1304
Contract Number RP200

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