Wilfrid A Nixon

Effects of Adverse Weather on Traffic Crashes: Systematic Review and Meta-Analysis

Adverse weather obviously has an impact on vehicle crash rates on roads and highways. However, it would be valuable to quantify the extent to which weather conditions affect the crash rate. To do that, a meta-analysis has been conducted to generalize research findings on this subject and attempt to quantify the impact of weather on traffic crashes. Studies between 1967 and 2005 that examined the interaction of weather and traffic safety were reviewed. Thirty-four papers and 78 records that meet the predetermined criteria were included in the analysis. Crash rates from each study were normalized with respect to effect size for meta-analysis generalization. Results indicate that the crash rate usually increases during precipitation. Snow has a greater effect than rain does on crash occurrence: snow can increase the crash rate by 84% and the injury rate by 75%. Further results also suggest that variations in study results can be explained by study design, date of the study, and region or countries included in the study.

Use of Abrasives in Winter Maintenance at the County Level

The use of abrasives in winter maintenance is a well-established practice. Typically, sand is placed on the road in amounts up to 340 kg/lane-km (1,200 lb/lane-mi). The sand is intended to increase friction between the vehicles and the often snow- or ice-covered pavement. Yet very little information exists on the value of sanding as a winter maintenance procedure. What information does exist tends not to support sanding as a process. Studies suggest that at highway speeds sand is swept off the road by relatively few vehicle passes (8 to 12) and that friction gains from sanding (when the sand remains on the road) are minimal. There are increasing environmental concerns about sanding. Some U.S. cities have already stopped sanding because of air quality concerns. Others are required to clean up all sand as soon as possible after application, using street sweepers. The state of the practice of abrasives usage in Iowa counties is reviewed. On the basis of these practices and the existing studies on abrasives usage, an attempt has been made to categorize the practices into three classifications: appropriate, questionable, and inappropriate. The choice of these categories for each practice is discussed. The classification of practices suggests that significant changes may be needed in regard to abrasives usage in winter maintenance. The nature of these changes is presented and discussed.

A Non-Linear Fatigue Damage Model for Concrete in Tension

Although concrete is used primarily because of its properties under compressive loading, a knowledge of its tensile behavior is essential in situations in which cracking, and the resulting change in stiffness, are critical for the service and ultimate load behavior of a structure. One important aspect of the tensile behavior of concrete is its performance under cyclic loading. The majority of past studies on the tensile fatigue performance of concrete have focused on the behavior under constant amplitude loads. However, in recent years, the effect of variable amplitude loading has also been emphasized. In this paper a model is presented for fatigue damage accumulation for concrete subjected to nonconstant tensile cyclic loads. The model is based on the concepts of Continuum Damage Mechanics and is able to account for the nonlinear propagation and accumulation of fatigue damage. Calibration of the model is done using existing experimental data, and its validity is checked against recently published tests.

Developing a Storm Severity Index

A primary goal in winter highway maintenance is to develop various maintenance processes so that quality control can be measured. If actions can be measured, they can be improved. A difficulty with this approach is that winter maintenance addresses the impacts of winter weather on the transportation system and that weather is inherently uncontrollable. Consequently, for a quality process to be applied to winter maintenance, the severity of individual storms must be assessed. This paper presents one way in which the severity of a storm can be measured, specifically by an index. The first step in developing an index for individual storms is to develop a method of describing storms. The method here describes storms by using six factors, including prestorm and poststorm conditions and temperatures, wind speed, and precipitation type. The matrix created is a refinement of that presented in FHWAs manual of practice for effective anti-icing. With the use of a simplified variation of this matrix-based descriptio...

Development and Use of an E-Mail-Based List-Serve for Winter Highway Maintenance

At the 4th TRB Symposium on Snow Removal and Ice Control Technology, held in Reno, Nevada, in 1996, it was suggested that some sort of centralized e-mail-based communications system would benefit the winter maintenance community. Later that year, the snow and ice list-serve was established (snow-ice@list.uiowa.edu). The performance of the list-serve in the three years since its formation is reviewed. Membership and message volumes are reported. Messages sent are divided into categories. The mechanics of the list-serve are described, and the procedures for its establishment and maintenance are detailed. There have been changes in procedure since the list’s formation, and these changes are discussed. Problems with the list are also presented and solutions are given. Estimates for the time required to maintain such a list-serve are given, along with details of the software used to establish and maintain the list. Finally, results of a survey of the list of subscribers are presented; on the basis of this, the value of the list-serve to the winter maintenance community is estimated. Information on how to subscribe to and use the list-serve is provided.