Official Title: Reducing Red Light Running Through Longer Yellow Signal Timing and Red Light Camera Enforcement: Results of a Field Investigation
Authors: Richard A. Retting, Susan A. Ferguson and Charles M. Farmer
This is a 2007 study by the Insurance Institute for Highway Safety(IIHS) on red-light cameras in the City of Philadelphia that compares the before and after red light violation statistics where there are 2 RLC intersections in that city. The study also alters the timing of Yellow Light signals during the pre-RLC period. The analysis uses 3 months of pre-RLC crash data compared to 16 months of post-RLC data. The statistics used in this analysis were collected by the IIHS and since there are no crash statistics gathered for this study there is no Distance-From-Intersection inclusion zone for crashes used. There are no data or conclusions in this report that suggest a reduction or increase in fatalities due to RLCs. This study does not cover injury crashes. Controls intersections are used for this study by analyzing several periods of video recordings of similar intersections several miles away from the treatment intersections. The conclusions arrived upon are: "Results showed that yellow timing changes reduced red light violations by 36 percent. The addition of red light camera enforcement further reduced red light violations by 96 percent beyond levels achieved by the longer yellow timing".
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This is a brief 12 page study, and the data appears to be valid, but the selection of 2 RLC intersections is very small for this kind of study. There is very minimal pre-RLC data(only 3 months) that substantially reduces the significance of this study, but the post-RLC data(16 months) is much more adequate. The changing of yellow light timings during the already limited pre-RLC period further compromises the results. The lack of raw crash statistical data being cited significantly reduces the value of this study since stronger compliance with red lights is never proven to equate to safer intersections. The limited conclusions are mostly supported by the data that is provided.
Philadelphia Weekly researched the crash data for these two RLC intersections and published an article detailing that crashes have increased 12% since the RLCs were installed. The data came directly from the Philadelphia Police Department and was available at the time of this IIHS study, although the authors of this study give no reason why they did not analyze the crash statistics for these intersections. The authors of this study work for the Insurance Institute for Highway Safety(IIHS), an organization sponsored by car insurance companies which make substantial amounts of money on RLC installations due to points being assessed on drivers licenses and higher crash rates, both of which lead to higher insurance premiums, as well as direct investment by some insurance companies in the companies that sell Red Light Camera systems themselves, so they have a very strong vested interest in presenting RLCs in a positive light and cannot be considered a neutral or impartial party on this subject.