Although during the past several years significant progress has been made in improving safety on U.S. highways, the frequency and severity of crashes continue to be of concern. A better understanding of the factors associated with crashes will facilitate the identification of suitable countermeasures that could further reduce the occurrence of crashes. Results are presented from a study that determines how the characteristics of speed, flow, and geometry affect the crash rates for two-lane highways. Deterministic models that relate the crash rate with the mean speed, standard deviation of speed, flow per lane, lane width, and shoulder width are presented. The multivariate ratio of polynomials method was used to develop the models. Research was limited to two-lane roadways in Virginia with speed limits of 89 km/h (55 mph). The data were obtained from speed-monitoring stations established by the Virginia Department of Transportation and from police accident reports from January 1993 to September 1995.
Work zones tend to cause hazardous conditions for drivers and construction workers, because they create conflicts between construction activities and traffic, thus exacerbating the existing traffic conditions. Every effort should therefore be made to minimize the negative impacts of work zones. A clear understanding of work-zone crash characteristics will help to determine appropriate measures to minimize work-zone hazards. This study investigated the characteristics of work-zone crashes that occurred in Virginia from 1996 through 1999. The information on each crash was obtained from police crash records. Each crash was located in one of five areas of the work zone—( a) advance warning, ( b) transition, ( c) longitudinal buffer, ( d) activity, and ( e) termination. The percentage distributions were analyzed relative to crash location, crash severity, collision type, and highway type. The proportionality test was used to determine significant differences at the 5% significance level. The results indicate that the activity area is the predominant location of work-zone crashes regardless of highway type, and rear-end crashes are the predominant crash type. The results also indicate that the proportion of sideswipe-in-same-direction crashes in the transition area is significantly higher than that in the advance warning area.
In work zones, drivers do not slow down in response to conventional signs. Changeable-message signs (CMSs) equipped with a radar unit can be used to display specific warning messages to speeding drivers. The radar unit detects the speed of each vehicle entering the work zone and can be programmed to activate the CMS if the speed of the vehicle exceeds a preset threshold value. A two-phase longitudinal study was conducted. The first phase, conducted by Garber and Patel, examined the short-term effectiveness of the CMS with radar in reducing vehicle speeds in work zones. The second phase, some of the results of which are presented, evaluated the influence of the duration of exposure of the CMS with radar on its effectiveness in reducing speeds in work zones. Speed and volume data for the population were collected at the study sites by automatic traffic counters placed at the beginning, middle, and end of each work zone. In addition, the speeds of individual drivers who triggered the CMS by exceeding the threshold speed were also recorded (using a video camera) at two other locations within the work zone for several weeks and analyzed. The results of the study indicated that the duration of exposure of the CMS does not have a significant impact on speed characteristics and driver behavior. Therefore, the CMS continues to be effective in controlling speeds in work zones for projects of long duration. The results also indicated that the CMS with radar reduces the probability of speeding at work zones and that this effect is maintained for at least up to 7 weeks.
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