A joint econometric analysis of seat belt use and crash-related injury severity

Abstract

This paper formulates a comprehensive econometric structure that recognizes two important issues in crash-related injury severity analysis. First, the impact of a factor on injury severity may be moderated by various observed and unobserved variables specific to an individual or to a crash. Second, seat belt use is likely to be endogenous to injury severity. That is, it is possible that intrinsically unsafe drivers do not wear seat belts and are the ones likely to be involved in high injury severity crashes because of their unsafe driving habits.The preceding issues are considered in the current research effort through the development of a comprehensive model of seat belt use and injury severity that takes the form of a joint correlated random-coefficients binary-ordered response system. To our knowledge, this is the first instance of such a model formulation and application not only in the safety analysis literature, but in the econometrics literature in general. The empirical analysis is based on the 2003 General Estimates System (GES) data base. Several types of variables are considered to explain seat belt use and injury severity levels, including driver characteristics, vehicle characteristics, roadway design attributes, environmental factors, and crash characteristics. The results, in addition to confirming the effects of various explanatory variables, also highlight the importance of (a) considering the moderating effects of unobserved individual/crash-related factors on the determinants of injury severity and (b) seat belt use endogeneity. From a policy standpoint, the results suggest that seat belt non-users, when apprehended in the act, should perhaps be subjected to both a fine (to increase the chances that they wear seat belts) as well as mandatory enrollment in a defensive driving course (to attempt to change their aggressive driving behaviors).

Examining the influence of aggressive driving behavior on driver injury severity in traffic crashes

“…Further, young drivers are generally likely to sustain less severe injuries compared to older adults, with young adults (16-20 years of age) being the least likely to be severely injured. These results are similar to those reported in earlier studies of injury severity (see, for example, O'Donnell and Connor, 1996;Kim et al, 1994;Srinivasan, 2002;and Eluru and Bhat, 2007), but with one very important difference. As indicated in Chapter 1 of the thesis, the results from the earlier injury severity studies regarding gender/age effects would suggest that countermeasures should focus on reducing injury severity particularly for female drivers and older drivers.…”

“…Most of the recent injury severity studies have used an ordered-response discrete choice formulation to recognize the ordinal nature in which injury severity is typically recorded (for instance, "no injury", "possible injury", "non-incapacitating injury", "incapacitating injury", and "fatal injury"). A comprehensive review of different discrete variable studies of crash-related injury severity is provided in Eluru and Bhat (2007). In this chapter, we limit our review of injury severity studies to those very recent discrete choice studies that have not been listed in Eluru and Bhat, or are directly relevant to the aggressiveness-injury severity context of the current research effort.…”

“…The log-likelihood function then corresponds to separate components for these two models. The multidimensional integrals may be evaluated\d using now wellestablished Halton-based simulation techniques (see Eluru and Bhat, 2007, Bhat, 2003, Bhat, 2001). …”

“…Similarly, consider the case that seat belt non-users are generally aggressive drivers, as has been suggested by, among others, Cohen and Einav (2003), and Eluru and Bhat (2007). Seat belt non-usage, even after controlling for aggressive driver behavior, is likely to increase crash injury severity because of the "lack of restraint" effect.…”

A mixed generalized ordered response model for examining pedestrian and bicyclist injury severity level in traffic crashes

“…Also, it is not always straightforward to understand the impacts of the coefficients within the MGORL framework. To understand the impact of factors more clearly, we compute the aggregate level "elasticity effects" of variables (for more details see Eluru and Bhat 2007).…”