Official Title: ANALYSIS ON THE EFFECTIVENESS OF PHOTOGRAPHIC TRAFFIC SIGNAL ENFORCEMENT SYSTEMS IN TEXAS
Author: Troy D. Walden, Ph.D.
This is a 2008 study by the Center for Transportation Safety at the Texas Transportation Institute of Texas A&M University on the effects of red-light cameras in the city of Houston, Texas and several other cities in the state of Texas. This study compares the before and after crash statistics of 56 RLC intersections in that state. The study uses 6 to 12 months of pre-RLC crash data compared to up to 12 months of post-RLC data. The statistics used in this analysis are from various municipalities all with different reporting standards and the report did not define what they used as their Distance-From-Intersection inclusion zone for crashes. There are no data or conclusions in this report that suggest a reduction or increase in fatalities due to RLCs. The study concludes that: "While these results cannot conclusively determine that red light cameras are responsible for the overall reduction in crashes, it does appears that the presence of the treatment provided some effect on the frequency of crashes at the selected intersections for the limited time period of this analysis", and "Due to the short time period of analysis, no conclusions may be inferred from the pre or post-analysis with any statistical confidence".
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This is a 65 page report, the data and statistical analysis are not standard or thoroughly explained. The selection of 56 RLC intersections is large number of intersections for this kind of study. The lack of a defined Distance-From-Intersection inclusion zone for crashes somewhat diminishes the conclusions and consistency of the data. Their method of "annualizing" crash data in effect creates fake data in order to "fill in" the gaps in the data where they have less than 12 months of real crash data. This is something that is not standard in these studies and it greatly compromises this study and its validity. The before and after RLC date periods of 12 or less months of before and after-RLC data is less than optimal for this type of analysis. No raw crash data is available or referenced in this report. The crash data for this same time period in Houston used by this report for over half of its data set is also used as the crash data in the 2008 Houston Rice University RLC report which directly contradicts a large sample of the referenced data(external link). Not all of the conclusions of this study are supported by the data supplied.
Something else that should be mentioned is the the RLC crash data from the city of Lubbock, TX was specifically omitted from this study even though it fit the stated requirements of this study and the data was available to the author. No reason was given for this omission, and Lubbock is not mentioned anywhere in this study. Here is a report on the Lubbock, TX RLC system from 2008.