In a huge front-page story Friday, the Chicago Tribune published yet another installment in its long-running vendetta against the city’s photographic traffic enforcement program. Because the Trib chose to obscure key information about the severity of crashes, the story is worthless as an evaluation of the city’s red light camera program.
The article lavishes attention on a $14,000 study “commissioned by the Tribune [that] concluded the cameras do not reduce injury-related crashes overall.” But if you manage to get 2,000 words into the article, authors David Kidwell and Alex Richards acknowledge that nine years ago the Federal Highway Administration also commissioned a study on red light cameras. And if you take a close look at the FHWA study, it debunks the entire premise behind the Tribune’s analysis.
The FHWA employed a methodology that closely resembles the Tribune’s, with one all-important difference: The feds incorporated the severity of crashes into their calculations. Both studies found that red light cameras tend to prevent right-angle crashes while rear-end crashes increase. But since FHWA also acknowledged that right-angle crashes are more severe and impose higher costs on society than rear-end crashes, it found that even with increases in one crash type, the benefits of red light cameras outweigh the costs.
On its website explaining the FHWA study, the University of North Carolina’s Highway Safety Research Center clearly states: ”Since the angle and rear-end crashes are of different severities, you must combine both the change in frequency with differences in severity in the analysis. This is why looking… just at changes in total crash numbers is not correct.” While the Trib interviewed a UNC researcher about camera site selection, it failed to note this basic conclusion that upends the paper’s own methodology.
Put simply, the Tribune’s methodology ignores the most important factor – the number of people killed and the severity of injuries sustained at intersections with red light cameras.
The FHWA didn’t make that mistake. Factoring in “the lesser severities and generally lower unit costs for rear end injury crashes” the agency concluded that red light cameras achieved $14-18 million in savings to motor vehicle occupants in urban and rural intersections in seven municipalities. Only when mentioning the FHWA study – thousands of words into the piece – does the Tribune admit that there is a difference in severity of different crash types.
The Tribune also drew unwarranted conclusions from its own study, which found that the change in total crash numbers was not statistically significant. The study itself says “the increase in crashes may not necessarily be because of [adding red light cameras], but may just have happened by chance.”
But the data the Tribune collected is sufficiently robust to bolster the conclusion that red light cameras reduce right-angle crashes.
“[The] Chicago Tribune’s study confirms that these cameras help to reduce dangerous angle crashes that are more likely than rear-end crashes to cause serious injury or death,” Chicago Department of Transportation Commissioner Rebekah Scheinfeld said in a statement today, They’re less severe because they’re slower – drivers are decelerating, not cruising – and cars are better padded in the front and rear. Read more…