摘要：Objectives. We investigated how much time passes before gasoline price changes affect traffic crashes. Methods. We systematically examined 2004 to 2012 Mississippi traffic crash data by age, gender, and race. Control variables were unemployment rate, seat belt use, alcohol consumption, climate, and temporal and seasonal variations. Results. We found a positive association between higher gasoline prices and safer roads. Overall, gasoline prices affected crashes 9 to 10 months after a price change. This finding was generally consistent across age, gender, and race, with some exceptions. For those aged 16 to 19 years, gasoline price increases had an immediate (although statistically weak) effect and a lagged effect, but crashes involving those aged 25 to 34 years was seemingly unaffected by price changes. For older individuals (≥ 75 years), the lagged effect was stronger and lasted longer than did that of other age groups. Conclusions. The results have important health policy implications for using gasoline prices and taxes to improve traffic safety. More than 40 000 traffic fatalities have occurred in the United States every year from 1963 to 2007 (except in 1992; data available as a supplement to the online version of this article at http://www.ajph.org ). In 2008, US roadway deaths fell to 37 313, which is the lowest point since 1963 and is 9.1% lower than the 2007 rates. The recent decline in traffic fatalities started in 2005 and continued steadily through 2011, with a slight increase in 2012. This trend is similar in many other developed countries. Despite the steady decline in traffic fatalities, road crashes remain a major public health and economic concern worldwide. Road deaths are a calamity for all affected, and injuries can cause distress and have life-changing effects. In the United States, crashes resulted in an economic loss of $277 billion in 2010 and an additional $594 billion in social and health impacts related to loss of life and decreased quality of life owing to injuries. 1 Drunk driving resulted in a $49 billion economic loss and a $199 billion societal and health impact, and failing to use seat belts cost $14 billion and $58 billion, respectively. To help address these problems, the Moving Ahead for Progress in the 21st Century Law (Pub L. No. 112–141, 126 Stat. 405, HR 4348), enacted in 2012, requires states to increase their focus on transportation safety performance targets and implement programs that best use limited resources for reaching their goals. A large body of literature links traffic crashes to their contributing factors. Among those factors are road infrastructure 2,3 ; systems operations and management 4 ; road user behaviors such as seat belt use, drunk driving, and texting while driving 2 ; demographic and cultural changes, such as an aging population and the iPhone culture of the younger population 5 ; vehicle safety advancements 6,7 ; emergency response and trauma care advancements 8 ; and training and education campaigns and law enforcement interventions. 9,10 The literature also suggests that economic conditions are a contributing factor in traffic crashes; that is, when the economy grows, people drive more often and with less reserve, which results in more traffic crashes. 11 States with higher per capita income have higher traffic-related fatality and injury rates. 2,8 However, when the economy declines, people drive less frequently and more conservatively, resulting in safer traffic conditions. Three tangible links between the economy and traffic safety are income, unemployment rates, and gasoline prices. Lower-income drivers are limited in their ability to buy gasoline, which reduces the frequency and distance of their trips. They might also reduce frequent single-purpose trips in favor of multipurpose trips taken less often. Some may even forego automobile ownership. Likewise, the higher unemployment rates that occur in a weak economy mean fewer work-related trips and could have many of the effects that lower income has. A limited but increasing body of literature associates fewer traffic crashes with higher gasoline prices or taxes. 12–24 Overall, studies found a positive association between gasoline prices and traffic safety. Increased gasoline prices improve traffic safety by discouraging the amount of driving and by encouraging safer driving behavior. 12 Specifically, when gasoline prices are high, drivers might reduce non–work-related trips and switch to carpooling or public transportation. 17 Drivers also might drive in a more fuel-efficient manner by accelerating and braking more conservatively, thus reducing the rate of traffic crashes. 12 The finding of the positive association between gasoline prices and traffic safety applies to total crashes, fatal crashes, and drunk-driving crashes; however, as gasoline prices increase, people retreat to less expensive modes of transportation, such as motorcycles, which in turn leads to more motorcycle crashes. 23 In addition, the association between gasoline prices and traffic safety varies by age, gender, and race. Gasoline prices have a greater impact on younger drivers than on older drivers, a slightly greater impact on female drivers than on male drivers, and a similar impact on White drivers and Black drivers. What remains an open question, though, is how long it takes before gasoline price increases affect traffic safety. Although some studies found both short-term (immediate) effects and long-term (lagged) effects, 12,13,15,16,18 the lag, which is the difference in time between gasoline price at a point and crashes at a later point, was measured in yearly intervals and did not provide the necessarily fine calibration: the effects could change from month to month. Further, those studies were not designed to specifically and comprehensively explore the possible lagged effects that gasoline prices have on crashes. We systematically investigated how long it takes gasoline price changes to affect traffic crashes. We hypothesized that the effects take some time to occur because many commuting activities such as driving to work cannot be reduced immediately; it takes time for drivers to find alternatives. We further hypothesized that the effects vary across the stages of life because reducing travel costs in response to higher gasoline prices is prioritized at different levels in relation to income, responsibilities, life goals, and others factors.
