Pinpointing the causes of a vehicle crash, and any fatalities or serious injuries that occur in
crashes, is a very difficult task. Many variables can contribute to one vehicle model having a
higher risk on-road risk than another model; these variables can be grouped into three general
categories, driver characteristics and behavior, vehicle attributes and condition, and crash
location and environment.
The 2003 NHTSA study (Kahane, 2003) did a thorough job accounting for many of the variables
that may affect injury and fatality outcomes in crashes. However, even this comprehensive
analysis did not account for all of these variables; indeed, it may not be possible to fully account
for all of the important variables that determine crash outcomes. I have critiqued this analysis in
comments submitted for previous NHTSA rulemakings (Wenzel and Ross, 2004a; Wenzel and
Ross, 2004b; Wenzel and Ross, 2005; Wenzel and Ross, 2008).