In 2010, 16.5 percent of all fatal vehicle crashes in Iowa involved large trucks compared to the national average of 7.8 percent. Only about 16 percent of these fatalities involved the occupants of the heavy vehicles, meaning that a majority of the fatalities in fatal crashes involve non-heavy truck occupants. These statistics demonstrate the severe nature of heavy truck crashes and underscore the serious impact that these crashes can have on the traveling public. These statistics also indicate Iowa may have a disproportionately higher safety risk compared to the nation with respect to heavy truck safety. Several national studies, and a few statewide studies have investigated large truck crashes, however no rigorous analysis of heavy truck crashes has been conducted for the state of Iowa. This thesis uses the most current statewide crash data to perform an in-depth analysis of heavy truck crashes in Iowa. The objective of this study is to investigate and identify the causes, locations, and other factors related to heavy truck crashes in Iowa.

To conduct this study, crash data for the years of 2007-2012 for the state of Iowa were used to develop statistical models for single and multiple vehicle heavy truck crash severity. Single vehicle crashes were modeled using a binary probit model with outcomes of injury (fatal, major, minor, or possible injury) or no injury (property damage only). Multiple vehicle crashes were modeled using a nested logit model with severity outcomes of severe injury (fatal or major injury), minor injury (minor or possible injury), and no injury (property damage only), with the two injury outcomes placed in a nest.

Findings from the two models were both complimentary and contradictory. Both models found older drivers to be associated with more severe injuries. Both models also indicated crashes impacting and damaging the front of both heavy trucks and non-heavy trucks to play a significant role in the severity outcome of the crash. The main disparity of the two models relates to the effect single unit and combination trucks have on crash severity, with combination trucks increasing the probability of a severe injury in the multiple vehicle model and single unit trucks increasing the probability of an injury in single vehicle crashes. Other factors found to be significant in either of the two models relate to the manner of the collision, temporal factors (season, day of week, time of day), vehicle characteristics, roadway characteristics, and environmental factors.