Accidents at Red Light Cameras in Chicago – City’s Data (Part 4 of a Report on Red Light Cameras in Chicago)
Part 1 of this report considered accident trends in Chicago between 2001 and 2008. Part 2 focuses on accidents at traffic signals. Part 3 offers data on accidents at red light camera intersections based on IDOT data.
This part analyzes accident data obtained from the city of Chicago. The city’s study looks at 20 RLC intersections and 20 control intersections and compares them. The control intersections are supposed to be similar intersections to the RLC intersections in terms of traffic and accident rates. By using control intersections, it is possible to isolate the effect of the red light cameras from other factors affecting accidents, e.g., people driving less.
The study compares the accidents 1 year prior to the startup date to accidents 1 year after the start up date for the red light cameras. In evaluating the study, we had to eliminate 10 of the intersections, both control and RLC, because they did not have a full 12 months of prior data. This left us with 10 control intersections and 10 RLC intersections.
The control group experienced a 3.8% decrease in accidents, while the RLC group experienced a 5.3% decrease in accidents. In sum, there was only a 1.5% different attributable to the RLCs. This suggests a very small benefit for the RLCs. This decrease is a much smaller figure than the city claims.
This study was conducted entirely by the city of Chicago. The report is dated October 2007. The departments involved were the OEMC and the Traffic Management Authority. The study was not made public. I received the data after a FOIA request that required the assistance of the Illinois ACLU to push the city to release this information.
I cannot vouch for the accuracy of this study. The city picked the camera locations to study. I have no idea if they tried to “massage” the data to gain beneficial results. The city is planning a followup report due later this summer. As far as I know, they do not having any impartial experts involved in the process. I hope the city’s analysis will be fair, rather than manipulating the data to justify the effectiveness of the red light cameras.
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