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Evaluation of Crash Rates and Causal Factors for High-risk Locations on Rural and Urban Two-lane Highways in Virginia
Kassebaum, Elizabeth Abel.
Nicholas J. Garber
Year: 2008
VTRC No.: 09-R1
Abstract: Considerable efforts have been made in recent years to make highway travel safer. Traffic engineers continue to emphasize the identification of causal factors for crashes on individual sections and on different functional classes of highways as an area of emphasis. If precise causal factors and corresponding countermeasures can be identified, traffic engineers in the roadway design field would be able to use that information to make Virginia's highways safer. The purpose of this study was to identify causal factors of crashes on two-lane highways and corresponding effective countermeasures that should significantly reduce these crashes. The scope of the research was limited to two-lane highways in Virginia with data from 2001 through 2004. The researchers identified 143 five- to ten-mile stretches of two-lane highways in Virginia that proportionally represented each of the counties in Virginia. Relevant data elements that included time of crash, road and weather conditions, driver action, and type of collision were extracted from the relevant police reports. Traffic volumes and speed data were obtained from VDOT publications. Global positioning system data collected for each site provided information on grading and curvature of the sites. Signing and speed limit data were also collected for each site. The final dataset consisted of nearly 10,000 crashes and more than 30 variables, grouped under different highway classifications (urban primary, urban secondary, rural primary, rural secondary) and collision type (rear-end, angle, head-on, sideswipe, run-off-the-road [ROR], deer, and other). Fault tree analysis was used to identify the associated causal factors, and generalized linear models were developed from which the significant causal factors were identified. The results indicated that ROR crashes were the predominant type of crash, followed by rear-end, angle, and deer crashes. These crashes represented nearly 70% of all crashes. The significant causal factors for ROR crashes were found to be curvature and annual average daily traffic. One of the four recommendations is that a plan for correcting the geometric deficiencies of the significant causal factors at sites with high ROR crashes be developed and implemented. The economic benefits of improving the radii at locations with predominantly ROR crashes were investigated using a sensitivity analysis on the benefit/cost ratios for different levels of improvements and expected crash reductions. In all cases, the ratio was higher than 1, with a range of 1.16 to 9.60.