Official Title: PERFORMANCE AUDIT: RED LIGHT CAMERA PROGRAM
Authors: F. MICHAEL TAYLOR, CITY AUDITOR and VANESSA D’SOUZA SENIOR DEPUTY CITY AUDITOR
This is a 2007 report by the city auditor of the city of Stockton, California, USA on the effects of red-light cameras in the city of Stockton, California. This study compares the before and after crash statistics of 12 RLC intersections in that city. The study uses 12 months of pre-RLC crash data compared to 12 to 24 months of post-RLC data. The statistics used in this analysis are from the Stockton Police Department and the study does not define a fixed Distance-From-Intersection inclusion zone for crashes. This study uses crash data for all intersections in the city as control data. There are no data or conclusions in this report that suggest a reduction or increase in fatalities due to RLCs. The results show that total crashes at RLC-equipped intersections have increased by 10% as well as a 14% decrease in injury crashes for the first year after RLCs were installed at RLC intersections. The study concludes that : "Red light cameras have reduced the number of accidents and injuries as well as the seriousness of injuries.", and "City’s Red Light Camera Program is generating revenue".
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This is a brief 28 page study, the detail data per intersection per month is not included in this report, and the use of undefined partial-year data for the second year post-RLC greatly invalidates all comparisons made to the second year post RLC. In fact they state "We had insufficient data to make a conclusion regarding the 2 year period after implementation", yet they went ahead and made conclusions based on that exact data. Also, the selection of only 6 of the 12 RLC intersections for the injury statistics and analysis is never explained or justified, and it seems to disprove the conclusion that severity of injury crashes is going down. The before-RLC period is average and the after-RLC period is average for this kind of study. There are several mathematical errors in the calculations shown in this report for the data that is supplied. The conclusions assume partial-year data as total year data, which severely harms the validity of the analysis of pre-RLC data against the second year post-RLC data. The report explains the increase in crashes as being a function of increased population and traffic, but those increases over the 3-year data period are relatively very small compared to the increase in crashes. On the financial side, the conclusion that the program is "generating revenue" makes no mention of the true audited net profit from the system, and the numbers they use are only estimates and assume 100% payment of all fees, which is not confirmed in any way. Some of the conclusions are supported by the data that is supplied in this report.