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Monday
Sep082014

Red Light Camera Study - 2014

Here is a snippet of my followup red light camera study.  The full report contains more extensive details and you can run your own analysis at my MiningChi site.

Executive Summary:

Chicago leads the nation with over 380 red light cameras (RLCs) at 190 intersections.  Four years ago, I did a short study that showed accidents in Chicago decreased between 2001 and 2008.  In contrast, accidents at intersections with RLCs increased.  This result threw doubt on the city’s claims of significant accident reductions because of RLCs. I am now conducting a follow-up study by analyzing the accident data and ticket data between 2009 and 2012.

The results showed that accidents have gone down overall about 6%.  This is expected, since there has been a reduction of 8% in the miles driven in Chicago.  Consequently, for a safety intervention to be effective, it would need to exceed the overall accident decrease of 6%.

Analyzing RLCs that were placed during the study, it was found that in the first year after a camera was introduced, there was actually an increase of 5% for accidents at the intersection.  This result was based on a very small sample size of 11 cameras and should not be considered definitive. 

A second interesting finding about RLCs was that accidents dropped at RLC intersections at a rate of 11% between 2009-2012.  This translates into 250 fewer accidents at RLC intersections between 2009-2012. The drop is largely due to a one-year 7% drop in accidents at RLC intersections during 2012.  It’s not clear what the cause of the drop is or whether it will persist. Nevertheless, in 2012 RLC intersections became safer than other traffic signal intersections.

The third point focused on using ticket data to explain why they are not reducing accidents. I offered two explanations for this: the inconsistent ticketing, e.g., spikes, and the rarity of accidents.

The results here mirror my earlier study.  The findings here are mixed and at best, the RLCs have a slight reduction on accidents.  Despite the million of dollars invested in RLCs and half a billion dollars in tickets, there is no evidence that the RLCs have had a significant safety benefit.

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