Investigating Peltzman Effects in Adopting Mandatory Seat Belt Laws in the US: Evidence from Non-occupant Fatalities

This study investigates the Peltzman effects in adopting mandatory seat belt laws in the US. According to the Peltzman offsetting effect theory, seat belt laws make drivers feel more secure and drive more aggressively, which could cause additional crashes and fatalities. A set of panel data containing 50 US states and the District of Columbia for the years from 1983 to 1997 are analyzed using such panel data techniques as fixed effects and instrument variables. Fixed effects consider both dimensions of states and time while instruments variables are proposed to reduce the endogeneity problem. Most data were collected as part of a previous research project. The fatality rate of non-occupants, which refer to pedestrians and cyclists on the road rather than drivers and passengers in the vehicle, is chosen as the dependent variable. The Peltzman effects are identified especially in the situation when the primary enforcement is directly introduced to a state. Moreover, sensitivity analyses on seat belt laws and seat belt usage are conducted to check the robustness of the results on Peltzman effects. Furthermore, the dynamics of Peltzman effects is examined by constructing variables that represent the amount of time seat belt laws have been implemented in a state. The Peltzman effects are found to fade away over time, which could be a reason many previous studies failed to identify the Peltzman offsetting effects caused by seat belt laws.