Karl H Zimmerman

EFFECT OF YELLOW-INTERVAL TIMING ON THE FREQUENCY OF RED-LIGHT VIOLATIONS AT URBAN INTERSECTIONS

Statistics indicate that red-light running has become a significant safety problem throughout the United States. There is a wide range of potential countermeasures to the problem of red-light running; an increase in yellow duration is one countermeasure. The objective of this research was to quantify the effect of a change in yellow-interval duration on the frequency of red-light violations. A before-after study is described and the resulting data are used to quantify the effect of increasing the yellow interval on the frequency of red-light violations. Based on this research, it was concluded that (a) an increase of 1.0 s in yellow duration (such that it does not exceed 5.5 s) will decrease the frequency of red-light violations by at least 50%; (b) drivers do adapt to the increase in yellow duration, but this adaptation does not undo the benefit of an increase in yellow duration; and (c) increasing a yellow interval that is shorter than the value obtained from a proposed recommended equation published by the Institute of Transportation Engineers is likely to yield the greatest return (in terms of a reduced number of red-light violations) relative to the cost of retiming a yellow interval in the field.

Driver Injury Severity Resulting from Single-Vehicle Crashes Along Horizontal Curves on Rural Two-Lane Highways

Horizontal curves have been identified as a target area for improving safety on rural two-lane highways in Texas. This study involved the development of multinomial logit models to assess driver injury severity resulting from single-vehicle crashes on such roads. Likelihood ratio tests warranted the development of separate injury severity models for curves of small, medium, and large radius. Various driver, vehicle, roadway, and environmental characteristics were found to affect injury severity among the 10,029 crashes analyzed. Run-off-the-road crashes, particularly those resulting in collisions with roadside objects, were found to increase injury severity significantly. Females were more likely to sustain injury and older drivers to be critically injured, particularly on curves of smaller radius. Various driver actions and behaviors were also significant determinants of injury severity. Unbelted drivers were up to 10 times more likely to suffer fatal injuries, and drivers who were uninsured, fatigued, or under the influence of drugs or alcohol were more likely to be seriously injured. Several of these behavioral factors were more pronounced on sharper curves.

Additional Dilemma Zone Protection for Trucks at High-Speed Signalized Intersections

Trucks are typically overrepresented in rural intersection crashes. These heavy vehicles have different stopping characteristics from the passenger cars around them, and such differences can result in conflicts and crashes. Crashes between trucks and passenger cars may be particularly severe. Trucks may require 50% more distance to stop than passenger cars, so they probably have a different dilemma zone than passenger cars. In addition, truck drivers may be less willing to stop for a red signal, and trucks are about twice as likely as passenger cars to run red lights. This paper presents the concept of providing additional dilemma zone protection for trucks by allowing for the additional time and distance that trucks require to stop and thereby reducing the number of trucks in the dilemma zone and red light violations. The concept was tested by using the detection control system developed at the Texas Transportation Institute. The use of a truck dilemma zone 1.5 s longer than the passenger car dilemma zone produced a 47% reduction in the number of trucks in the dilemma zone without a noticeable effect on intersection delay.

Intersection Safety at High-Speed Signalized Intersections: Number of Vehicles in Dilemma Zone as Potential Measure

High-speed signalized intersections may have both safety and operational problems. The safety problems traditionally have been solved with the use of dilemma zone protection of some form. However, dilemma zone protection tends to be associated with an increasing chance of running the phase to its maximum allowable duration—a max-out. At max-out, any provided dilemma zone protection ceases and any number of vehicles may be in the dilemma zone, a situation that creates the safety problem the system was meant to prevent. Most methods for assessing the safety of intersections do not include an assessment of signal operations. Reducing the number of vehicles in the dilemma zone for an intersection approach should reduce the number of drivers who do not receive dilemma zone protection and thereby reduce the probability of crashes for those approaches. A theoretical method calculates the number of vehicles in the dilemma zone at the end of a green phase, which can then be used to compare real-world and theoretical performance of different detection systems. An illustrative example provides one such comparison. Also, a field data collection method is provided for the assessment of a signal system in operation.

Bayesian Analysis of the Effect of Horizontal Curvature on Truck Crashes Using Training and Validation Data Sets

The research on the effects of roadway geometry on truck crashes is relatively limited in comparison with predictive models developed for total vehicle crashes. The most common predictive models currently used are Poisson and negative binomial models. This study uses a negative binomial model but applies the full Bayes’ methods for improving model performance. To use Bayes’ methods successfully, a learning process was used to develop a final model, which was then compared with a separate validation data set to verify its accuracy. The data set used for this study is based on rural two-lane collector and arterial horizontal curves in Ohio, comprising 15,390 observations from crash records between 2002 through 2006. Specific areas of interest in this study include the impact of shoulder width, horizontal curve radius, curve length, and other traffic parameters. The final results indicate a significant increase in truck crashes due to both horizontal curvature and passenger vehicle volumes. The final models predictions were improved compared with the initial model, indicating that the learning process is a viable tool for future crash model development.

Roadside Safety Analysis Program: A Cost-Effectiveness Analysis Procedure

Brief descriptions are provided of a new cost-effectiveness analysis program, known as the Roadside Safety Analysis Program (RSAP), which was developed under NCHRP Project 22-9. RSAP is an improvement over existing cost-effectiveness analysis procedures for evaluation of roadside safety improvements, such as the procedures in the 1977 AASHTO barrier guide and the ROADSIDE program. RSAP improves on many of the algorithms in the procedures and provides a user-friendly interface to facilitate use. The program has undergone extensive testing and validation, including evaluation by an independent reviewer. It is anticipated that RSAP will be available to the public through the McTrans Center at the University of Florida.

Potential Updates to 2004 Green Book's Acceleration Lengths for Entrance Terminals

AASHTOs Policy on Geometric Design of Highways and Streets (Green Book) notes that drivers entering a highway from a turning roadway accelerate until the desired highway speed is reached. Because the change in speed is usually substantial, provision is made for acceleration to be accomplished on an auxiliary lane, called an acceleration lane, to minimize interference with through traffic and to reduce crash potential. The 2004 Green Book contains acceleration lane lengths. The procedure identified to reproduce these values assumed running speed for the limited-access highway and the ramp along with acceleration rates from 1930s studies. Potential acceleration length values were then calculated by (a) updating the assumptions within the identified procedure and (b) using spreadsheets that can generate second-to-second acceleration. Findings from recent studies were compared with the existing Green Book values and the calculated suggested acceleration lengths. The suggested lengths determined in this paper, which are based on more realistic speed assumptions, more current acceleration lengths, and findings from recent research, are longer than the values in the Green Book. The paper recommends that additional research be done on acceleration lengths to determine whether the Green Book values should be increased.

Investigation of Time into Red for Red Light-Related Crashes

This paper describes a research effort to determine the time into red of 63 red light-related crashes. From these 63 crashes, the relationship of time into red and the red light-related crash type is explored, as are relationships to other factors. From the red light-related crashes investigated, it was found that red light-related crash type was related to time into red. Other factors were not found to be related to time into red, although the sample size and selection method prevented any definitive findings. A brief discussion of the possible safety effectiveness of the all-red interval is also included. The time into red of red light-related crashes is related to the time into red of red light violations, so a characterization of red light violations and crashes is provided, along with suggested red light violation countermeasure classifications for each type of red light violation.

Identifying intersections with potential for red light-related safety improvement

The problem of red light running is widespread and growing; its cost to society is significant. However, the literature is void of quantitative guidelines that can be used to identify and treat problem locations. Moreover, there has been concern voiced over the validity of various methods used to identify problem locations, especially when automated enforcement is being considered. This paper documents the development of a procedure for identifying and ranking intersection approaches with the potential for improvement in the area of crashes related to red lights. One component of this procedure is a safety prediction model. A sensitivity analysis of this model indicates that red light-related crashes decrease with an increase in duration of the yellow interval and a reduction in the speed limit.

Detection, Control, and Warning System for Mitigating Dilemma Zone Problem

High-speed signalized intersections present a grave hazard to the traveling public. An important component of this hazard is variation in the process of deciding whether to stop or proceed that occurs in the dilemma zone. To mitigate the dilemma zone problem, an innovative vehicle-specific detection, control, and warning system (DCWS) is being developed. To reduce dilemma zone conflicts, DCWS uses detection of individual vehicle speeds to provide unique, speed-specific dilemma zone protection for each vehicle as it approaches a signalized intersection. Although protecting all vehicles would be ideal, under some situations such protection is not possible. To account for these situations, DCWS also uses a vehicle-specific in-pavement system to give advance warning to drivers who are going to be trapped in the dilemma zone. With hardware-in-the-loop simulations, the new DCWS outperforms conventional dilemma zone warning systems in terms of the number of vehicles in the dilemma zone, the number and percentage of vehicles requiring warning, and the number of warning events per hour.