That termination gave Gallagher the opportunity to compare traffic data from both situations: with and without cameras watching for drivers running red lights. Immediately after the referendum passed, all of Houston's cameras were turned off. So, when we see a reduction in accidents the next year at an intersection where there's a camera, we don't know if it's because of the camera or if it's just a naturally occurring reduction that would have happened anyway."Īn opportunity to offset that mean reversion occurred in the traffic data from 2014, when the camera program in Houston was abruptly shut down after a voter referendum. "With mean reversion, you'd expect these intersections that had spikes in accidents the previous year to naturally have fewer accidents the following year. "It sounds great in theory, to target resources at places where there have been spikes in accidents, but it makes it very hard to evaluate the effectiveness of the program," he said. If an intersection had an unusually large number of accidents one year, it could be expected-due to mean reversion, the tendency for trends to vary in ways that center on an average over time-that there would be fewer accidents the following year. However, Gallagher said, many prior studies into red-light cameras neglected a critical factor called mean reversion.
Because local authorities could choose where cameras were placed, often with the result that the cameras were installed at intersections with a higher number of recorded accidents. Houston, Gallagher said, has about 1,000 major intersections and only 66 with red-light cameras, even with the city's comparatively large red-light camera program. "As an economist, what struck me was that it wasn't at all obvious that this program should work." "In debates about this issue, one side argues that these cameras improve safety, while the other side is often concerned with having computers give out traffic tickets when there wasn't a police officer to see what happened," said Gallagher. In a paper published in the American Economic Journal of Economic Policy, Gallagher and University of Arizona researcher Paul Fischer examine the concept of offsetting risks using more than a decade's worth of data from one of the country's largest red-light camera programs in Houston, Texas. Gallagher, a faculty member in MSU's Department of Agricultural Economics and Economics in the College of Agriculture and the College of Letters and Science, wondered if he could narrow down an answer to that question.
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