It has long been established that adverse driver behavior, including behavior relating to distracted driving, propensities for risk taking, and disregarding traffic rules, have been critical determinants with regard to the likelihood of a vehicle crash and its resulting injury severity. Socio-economic/educational/cultural factors (e.g. social willingness to comply with the law) have significant positive effects on traffic related fatalities. Using crash data from Iran over a six-year period from January 1, 2006 to December 31, 2011, this paper estimates a mixed logit model (with possible outcomes of severe injury, minor injury, and no injury) to investigate the unsafe driving behavior effects on driver-injury severity in a vehicle collision on interprovincial routes. The methodological approach allows the parameters to vary across observations as opposed to a fixed parameter model. The results showed random effects of female drivers, separated bi-directional route and clear weather condition for no injury severity function, following too closely for minor injury function, and average annual daily traffic for severe injury function. Several factors were found to significantly increase the likelihood of severe injury crashes including disregarding traffic rules, exceeding the speed limit, improper overtaking/passing, and driving in an erratic and negligent manner. The results of this paper will further help decision makers to better understand the contributing factors on crash injury severity and implement treatments to reduce the crash severity and improve transportation safety.