Work zone safety has become a major concern to many highway agencies and the highway safety community is looking at various ways of improving the situation. Accordingly, this paper describes an application of ordered probit modeling methodology to identify the factors associated with the injury severity of work zone crashes using a state level dataset. According to the findings of the severity model, work zone crashes involving trucks, following too close, non deployment of airbags, sideswipe collision of the same direction vehicles, crashes occurring on roadway, and crashes occurred while vehicles were taking left/right turns in work zone area are some of the factors that are contributing towards higher injury severity in work zone crashes.

Work zone crashes have accounted for 9,900 fatalities in the United States in the last ten years. As the traffic demand on the highways is increasing, management of such traffic flows in work zones has become a challenging task for many highway agencies and understanding crash characteristics would be valuable for highway agencies in setting up proper traffic management plans at work zones based on the prevailing conditions. Accordingly, this study investigated characteristics of work zone crashes in Iowa, Kansas, Missouri, Nebraska and Wisconsin, states currently included in the Smart Work Zone Deployment Initiative (SWZDI) region. Work zone crash data were obtained from respective departments of transportations and crash data from years 2002 to 2006 were considered in this study. The characteristics related to work zone crashes such as environmental conditions, vehicles, crashes, driver, and roadway factors were analyzed for the combined states. Results showed that most of the work zone crashes occurred under clear environmental conditions as during daylight, no adverse weather, etc. Multiple-vehicle crashes were more predominant than single-vehicle crashes in work zone crashes. Primary driver-contributing factors of work zone crashes were inattentive driving, following too close for conditions, failure to yield right of way, driving too fast for conditions, and exceeding posted speed limits within work zones. Middle aged drivers were more involved in work zone crashes and most of the work zone crashes lead to Property Damage Only (PDO) crashes. In order to find the relation between crash severity and other variables a test of independency was performed between them using chi-square test methodology.

In the summer of 2011, a change in the Kansas laws came into effect, increasing the speed limit on a selected set of freeway sections from 70 mph to 75 mph. Higher speeds were thought to have economic benefits, mostly because the travel time reduction means people reach their destinations more quickly. In this study, the sections where the speed limits remained unchanged, are compared to freeway sections that have been influenced by speed limit increase, to evaluate safety effectiveness. The study utilizes the before-and-after study with comparison group method to assess the safety effects provided in the Highway Safety Manual (HSM). Two crash datasets, obtained by considering three years before and three years after the speed limit increase, were compared in order to evaluate the safety effects of the speed limit change. The crash modification factors (CMFs) were estimated, which showed that there was a 27% increase in total crashes and a 35% increase in fatal and injury crashes across all sections after the speed limit change, and these increases were statistically significant at 95% confidence level. These confounding results show that the speed limit increase has not been beneficial for traffic safety in Kansas, and hence it is important to be cautious in such future situations. Also, additional data have been presented which would be beneficial in identifying and understanding any behavior change in drivers following a speed limit increase.

Even though speed limits of gravel roads are typically set based on statutory guidelines, there are some instances where exceptions are allowed and in place. In the absence of detailed literature on the subject, this study made an effort to evaluate and compare two criteria used in setting speed limits on low-volume gravel roads, with the intention of providing guidelines for future use. Field speed data were collected at a number of straight, level sections of gravel roads in Kansas where there is sufficient sight distance. Several sites located in two adjoining counties that use two different criteria for setting speed limits were also specifically selected for comparison purposes. One of the two counties adopts 35-mph speed limits on gravel roads and posts speed limit signs similar to those on paved roads. Characteristics of gravel roads in the adjoining county are very similar except that the speed limit is governed by the statutory limit (55 mph) and not posted. Collected actual speed data indicated no significant differences between the two speed data sets. In addition to operational speed comparisons, crash experience was also taken into consideration, which showed no major differences in terms of safety. When looking at the findings of this study, it is clear that lowered, posted speed limit values on gravel roads have not necessarily helped in improving either operational conditions or safety. Rather, reduced posted speed limits on gravel roads have increased the percentage of speed limit violators. Accordingly, care should be taken in making such decisions in the future for new situations.