Business recession and U.S. motor vehicle traffic deaths: A state space time series analysis

Purpose: U.S. motor vehicle traffic deaths sharply decreased in the last three years. The recent business recession is one likely reason for the decrease, but higher gasoline prices among other factors might also have contributed. The relative importance of these factors will be examined by state-space time series models.

Method: The analysis is based on U.S. monthly motor vehicle traffic death counts reported by FARS, 1/1994-12/2008 (n=180). Two series are examined: (1) all types of motor vehicle traffic deaths and (2) the former series with motorcyclists' deaths removed. State-space time series analysis is employed to model level, season and seven predictor series. The monthly predictor series are: (1) the civilian unemployment rate, (2) average retail gasoline prices in constant dollars, (3) percent of motor vehicle traffic deaths, ages 16-24, (4) percent of motor vehicle traffic deaths at dark, (5) average precipitation amounts, (6) average surface temperatures, and (7) a dummy variable designating the months of February in leap years.

Results: The analysis indicates that a 1% increase in the unemployment rate is related to a 2.1% (t=1.96; p<.05) reduction in all motor vehicle traffic deaths and a 2.9% (t= 2.52; p<.01) reduction when motorcyclists' deaths are excluded. The estimates are somewhat lower when the analysis adjusts for vehicle miles travelled.

Conclusions: The current business recession has had a strong depressing effect on motor vehicle traffic deaths. Full economic recovery may result in more then 4,000 traffic deaths per year.