Book Description

Large trucks play a key role in the overall safety of the highway transportation system. Previous studies have shown that in Ohio large trucks are over-represented in crashes that lead to serious and fatal injuries. A previous study that analyzed factors affecting truck-related crashes in Ohio found that posted speed limit and speed-related factors were among the significant factors impacting crash severity of truck-related crashes. Several studies have shown that increasing speed limits on roadways has a significant impact both on safety and operating speeds. On July 1, 2013, the Ohio0́9s legislature raised the speed limits on rural freeways from 65 mph to 70 mph for passenger vehicles, buses and trucks and to date the safety impact of this speed limit raise has not been evaluated. The current study investigated the impact of raising the speed limit on crash severity specifically with interest in large trucks and buses on rural freeways in Ohio. Statewide crash data from January 1, 2010 to December 31, 2018 were obtained from the Ohio Department of Public Safety (ODPS). Given that the numbers of rural freeway segments located all over the state and traffic volumes for each segment over the study period are not easily obtainable; therefore, the use of standard observational before/after study Empirical Bayes (EB) method was not feasible for the current study. Because of the model requirement for stationarity on a response series, this study utilized the Autoregressive Integrated Moving Average (ARIMA) time series intervention analysis method using monthly and seasonal crash data. A time series statistical method takes care of differences in crashes occurring in different years and recognizes trends in different periods of times. Time series analysis is a statistical technique that deals with time series data or trend analysis. Time series data means that data is in a series of time periods or intervals. Results of the current study show that the increase of speed in the selected segments of Ohio rural freeways has an impact on the frequency and severity of crashes associated with large trucks and buses. Moreover, the study found that weather conditions such as a bad winter has a significant impact on the frequency and severity of crashes associated with large trucks and buses as they happen to be higher during winter seasons as compared to other times of the year.