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Persaud B.,Ryerson University | Lyon C.,Persaud and Lyon Inc. | Eccles K.,VHB Engineering NC | Soika J.,VHB Engineering NC
Journal of Transportation Engineering | Year: 2016

The combined application of centerline and shoulder rumble strips is intended to reduce the frequency of crashes by alerting drivers that they are about to leave the traveled lane. To date, this combination treatment has not been rigorously evaluated with a multistate database. To fill this void, this study evaluated treated two-lane rural road locations in three states. To account for potential site selection bias, an empirical Bayes (EB) before-after analysis was conducted. The combined results for all states indicate statistically significant crash reductions for all crash types analyzed. The crash type with the smallest crash modification factor (CMF) (i.e., the greatest crash reduction) is head-on with a CMF of 0.632 (i.e., a crash reduction of 36.8%). For run-off-road, head-on, and sideswipe-opposite direction crashes combined (i.e., lane departure crashes), the estimated CMF is 0.733. Benefit:cost (B:C) ratios were estimated to range from 28.2 to 67.7, depending on the treatment cost and service life assumption. © 2016 American Society of Civil Engineers.


Torbic D.J.,Midwest Research Institute | Harwood D.W.,Midwest Research Institute | Bokenkroger C.D.,Midwest Research Institute | Srinivasan R.,Highway Safety Research Center | And 3 more authors.
Transportation Research Record | Year: 2010

A coordinated effort is under way to develop a Highway Safety Manual (HSM) for use in making quantitative estimates of the safety performance of specific highway types and quantitative estimates of proposed improvements to specific highway types. The highway types being addressed in the first edition of HSM are rural two-lane highways, rural multilane highways, and urban and suburban arterials. Explicit consideration of pedestrian safety on urban and suburban arterials is considered critical to implementation of the first edition of HSM. The objective of the present research was to develop a methodology for quantifying the effects of existing site characteristics and proposed improvements on urban and suburban arterials on pedestrian safety. The pedestrian safety prediction methodology has been developed to function as a component of the overall safety prediction methodology for urban and suburban arterials proposed for the first edition of HSM. In the present research, a methodology for prediction of vehicle-pedestrian collisions at signalized intersections was developed. This methodology includes base models for three- and four-leg signalized intersections and several accident modification factors.


Gross F.,Vanasse Hangen Brustlin Inc. | Lefler N.,Vanasse Hangen Brustlin Inc. | Lyon C.,Persaud and Lyon Inc. | Eccles K.,Vanasse Hangen Brustlin Inc.
Transportation Research Record | Year: 2010

Low-cost safety strategies that states may implement as part of their Strategic Highway Safety Plans need to be evaluated. FHWA organized a Pooled Fund Study of 26 states to evaluate several low-cost safety strategies, including the installation of advance street name signs at signalized intersections. This study investigates whether advance street name signs reduce crashes related to way-finding (i.e., rear-end and sideswipe crashes) at signalized intersections. Geometric, traffic, and crash data were obtained for signalized intersections at 82 sites in Arizona, 65 sites in Massachusetts, and 46 sites in Wisconsin. To account for potential selection bias and regression to the mean, an empirical Bayes before-after analysis was used. The analysis found no significant effect of advance street name signs on total crashes. However, the analysis indicated a significant reduction in sideswipe crashes, including a 27% reduction in Massachusetts and a 10% reduction for the three states combined. A disaggregate analysis was also conducted to identify differential effects. On the basis of conservative cost estimates, a reduction of just 0.01 crash per intersection year would achieve a 2:1 benefit-cost ratio. Given the low cost of this strategy and the potential to enhance way-finding, the use of advance street name signs is justified, particularly at three-legged intersections and locations with relatively large average annual daily traffic or a large expected number of crashes.


Persaud B.,Ryerson University | Lyon C.,Persaud and Lyon Inc. | Gross F.,Vanasse Hangen Brustlin Inc. | Eccles K.,Vanasse Hangen Brustlin Inc.
Transportation Research Record | Year: 2010

This study is a safety evaluation of offset improvements for left-turn lanes, a treatment intended to reduce the frequency of crashes by providing better visibility for drivers who are turning left. Geometric, traffic, and crash data were obtained for installations in Nebraska, Florida, and Wisconsin and for a number of untreated reference sites in each state. To account for potential selection bias and regression to the mean, an empirical Bayes before-after analysis was conducted. There was a large difference in observed effects in the three states, which may be explained, in part, by the variety of offset improvements applied. Florida and Nebraska employed pavement-marking adjustments or minor construction to improve the offset, but most improvements did not result in a positive offset. Wisconsin, conversely, reconfigured left-turn lanes throughmajor construction projects and realized significant positive offsets. Wisconsin showed significant reductions in all crash types investigated (total reduction, 34%; injury, 36%; left turn, 38%; and rear end, 32%), while results in Florida and Nebraska showed little or no effect on total crashes. For Nebraska, however, a disaggregate analysis did reveal that the percentage reduction in crashes increases as the expected number of crashes increases. An economic analysis indicated that offset improvement through reconstruction is cost-effective at intersections with at least nine expected crashes per year and in which left-turn lanes are justified by traffic volume warrants.


Srinivasan R.,University of North Carolina at Chapel Hill | Lyon C.,Persaud and Lyon Inc. | Persaud B.,Ryerson University | Baek J.,Korea Institute of Construction Technology | And 3 more authors.
Transportation Research Record | Year: 2012

This study estimated crash modification factors (CMFs) from before-after evaluations of two treatments targeted at reducing left-turn crashes at signalized intersections: (a) changes from permissive to protected-permissive phasing and (b) the implementation of a flashing yellow arrow for permissive left turns. Results of the first evaluation-based on 59 intersections in Toronto, Ontario, Canada, and 12 in North Carolina-indicated a substantial reduction in left-turn opposing through crashes, especially at intersections at which more than one leg was treated, and a small percentage increase in rear-end crashes. For the second evaluation (the implementation of the flashing yellow arrow)-based on data from 51 signalized intersections in Oregon, Washington State, and North Carolina-the results indicated a safety benefit at locations with some kind of permissive left-turn operation before and a disbenefit at locations that had a protected-only operation before. The study estimated the standard deviation of the distribution of the CMF in addition to the conventionally estimated standard error of the mean CMF value. For several CMFs, the standard deviation of the distribution was larger than the standard error of the mean value of the CMF and indicated a substantial variation in the effect of the treatment across different sites. This finding indicates the need for further research into the development of crash modification functions instead of CMFs and for the use of large treatment databases to undertake a more extensive disaggregate analysis of the safety effects. The finding also emphasizes the importance of providing a more explicit consideration of CMF variability in future editions of the Highway Safety Manual.

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