Persaud and Lyon Inc.

Toronto, Canada

Persaud and Lyon Inc.

Toronto, Canada
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Lyon C.,Persaud and Lyon Inc. | Persaud B.,Ryerson University | Himes S.,VHB
Transportation Research Record | Year: 2017

Data on traffic volumes are required to estimate the safety performance functions (SPFs) used to develop crash modfication factors and for various safety management applications. Estimation of SPFs for motorcycle crashes can be especially challenging because few jurisdictions collect motorcycle traffic volume data systematically. To address this challenge, analyses with data from Florida, Pennsylvania, and Virginia were conducted to explore how much predictive power for an SPF was lost when motorcycle traffic volumes were not known. The results of the analyses showed that when motorcycle volumes were unknown, the use of total annual average daily traffic on its own was sufficient to develop motorcycle crash SPFs. The potential bias from missing motorcyclespecific annual average daily traffic was sufficiently negligible where it existed, not to preclude SPF development. A more significant issue in the development of motorcycle crash SPFs is to work with a crash type that is relatively rare, so that SPFs cannot be developed for all motorcycle crash types or site types.


Zegeer C.,University of North Carolina at Chapel Hill | Lyon C.,Persaud and Lyon Inc. | Srinivasan R.,University of North Carolina at Chapel Hill | Persaud B.,Ryerson University | And 8 more authors.
Transportation Research Record | Year: 2017

The objective of this study was to develop crash modification factors for four treatment types: rectangular rapid-flashing beacon (RRFB), pedestrian hybrid beacon (PHB), pedestrian refuge island (RI), and advance yield or stop markings and signs (AS). From 14 cities throughout the United States, 975 treatment and comparison sites were selected. Most of the treatment sites were selected at intersections on urban, multi-lane streets, because these locations present a high risk for pedestrian crashes and are where countermeasures typically are needed most. For each treatment site, relevant data were collected on the treatment characteristics, traffic, geometric, and roadway variables, and the pedestrian crashes and other crash types that occurred at each site. Cross-sectional regression models and before-after empirical Bayesian analysis techniques were used to determine the crash effects of each treatment type. All four of the treatment types were found to be associated with reductions in pedestrian crash risk, compared with the reductions at untreated sites. PHBs were associated with the greatest reduction of pedestrian crash risk (55% reduction), followed by RRFBs (47% reduction), RIs (32% reduction), and AS (25% reduction). The results for RRFBs had their basis in a limited sample and must be used with caution. © 2017, National Research Council. All rights reserved.


Turner S.,University of Canterbury | Persaud B.,Ryerson University | Lyon C.,Persaud and Lyon Inc.
Road and Transport Research | Year: 2011

Comparisons of crash frequencies often seek to establish how a country is performing relative to others in road safety experience. While such comparisons can be quite useful from a high-level management perspective, they are less useful in comparing the relative safety of roadway designs within and among countries at a road element (e.g. signalised intersection) level. This paper has been prepared with two fundamental objectives in mind. Comparisons of selected crash prediction models from New Zealand, North America, Sweden, Italy and Australia are made to: 1) illustrate how such comparisons might be used to learn lessons from differences in crash experience for similar roadway elements, and 2) illustrate how to assess the transferability of these models among jurisdictions (countries or states). The results show that it is possible to transfer models from one jurisdiction to the next. However, there are a number of differences between jurisdictions as a result of different reporting rates, design standards, speed limits and climate conditions that need to be accounted for when transferring models.


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.


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. | Bagdade J.,Opus International Consultants Inc. | Ceifetz A.,Opus International Consultants Inc.
Transportation Research Record | Year: 2013

This paper documents the evaluation of the safety performance of passing relief lanes. A passing relief lane is an intermittently spaced additional lane on a two-lane road that provides drivers the opportunity to pass without having to cross into opposing traffic. The operational benefits are well known, but there is limited substantive evidence on the safety of these lanes. The study was based on data from Michigan, specifically traffic volume and crash history data for seven sites at which passing lanes were implemented within the study period, and for 100 reference sites (without passing lanes) and 231 passing lanes sites that existed throughout the study period. The analysis involved an empirical Bayes before-after evaluation and a comparative, cross-sectional evaluation of safety performance of locations with and without passing lanes. The methodologies were also applied to adjacent nontreated sites 1 mi upstream and downstream of the passing relief lane segment to examine possible spillover effects. From the results, crash modification factors (CMFs) were established for passing lanes in Michigan. These CMFs, which indicated significant safety benefits from passing relief lanes, may be considered for use in locations in other jurisdictions. The results from the cross-sectional and before-after evaluations were generally consistent.


Lyon C.,Persaud and Lyon Inc. | Persaud B.,Ryerson University | Merritt D.,The Transtec Group Inc.
International Journal of Pavement Engineering | Year: 2016

It is fairly well understood that there is link between pavement friction and safety, or more specifically, the probability of wet-weather skidding crashes. However, robust knowledge on the comparative quantitative effects on safety for specific treatments that improve pavement friction, which can assist pavement engineers in economically justifying and prioritising treatments, is sparse. The large-scale study on which this paper is based aimed to firm up this knowledge for a variety of low-cost treatments and road classes, using state-of-the-art methodology and substantial, high-quality data-sets. This was a retrospective study for pavement safety performance, looking back at crash data before and after treatments was implemented. Both flexible and rigid pavement treatments were analysed and crash modification factors were estimated for several target crash types and road classes. The majority of the friction improvement treatments considered under this effort are typically used for pavement preservation or minor rehabilitation purposes. Although pavement engineers recognise that these treatments generally improve safety, they are not typically installed by highway agencies explicitly for safety improvement objectives. The combined results for most treatment types confirmed nevertheless the safety benefits for wet-road crashes, with a few exceptions. For dry road crashes, there was some evidence of the deleterious effects of speed adaptation to new surfaces in that crashes increased for a few treatments on some road types. © 2016 Informa UK Limited, trading as Taylor & Francis Group


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 VHB Inc. | Lyon C.,Persaud and Lyon Inc. | Persaud B.,Ryerson University | Srinivasan R.,University of North Carolina at Chapel Hill
Accident Analysis and Prevention | Year: 2013

Roundabouts may be new builds but often are conversions from existing intersections. When contemplating the later, there is a need to estimate the safety effects of conversions. Several studies have estimated large reductions in crashes and severity; however, these results pertain mainly to conversions from unsignalized intersections. Results for conversions from signalized intersections have been less conclusive or consistent and tend to be somewhat dated. The objective of this study was to fill this void by estimating the safety effectiveness of converting signalized intersections to roundabouts. Several states helped to identify signalized intersections that were converted to roundabouts in the recent past. In total, 28 conversions were identified in the United States. The empirical Bayes (EB) method was employed in an observational before-after study to estimate the safety effects. Data from select states were also used in a cross-sectional analysis to investigate the compatibility of results from cross-sectional and before-after studies. The EB results indicated a safety benefit for converting signalized intersections to roundabouts. There were reductions in both total and injury crashes, with a larger benefit for injury crashes. Further analysis indicated that the safety benefit of roundabouts for total crashes decreased as traffic volumes increase, a result that suggests the need for the development of a crash modification function, a task for which more data would be required. The safety benefit for injury crashes was sustained across all traffic volumes. Both trends were supported by the cross-sectional analysis. Based on the analysis, it appears that roundabouts have the potential to significantly reduce crashes and severity at signalized intersections. A key aspect of the study was the estimation of the standard deviation of the distribution of the CMF in addition to the conventionally estimated standard error of the mean CMF value. For some CMFs, especially the CMFs for total crashes, the standard deviation of the distribution was larger than the standard error of the mean value of the CMF, indicating substantial variation in the treatment effect across sites. © 2012 Elsevier Ltd.


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.

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