Smart Cameras Blog

The is the first of a series of posts on report on red light cameras in Chicago.

The two important points:

1. Accidents are down 21% between 2001 and 2008, largely due to people driving less.

2. Any analysis of accidents needs to account for this trend. This trend suggests fewer accidents at construction zones, school zones, highways, and traffic signals (EVERYWHERE). If you are suggesting anything has contributed to safety, e.g., red light cameras, you need a control group to identify the contribution of the safety device or program. Otherwise it will appear that red light cameras have led to a drop of 20% in accidents (when the drop is due to other factors).

Lets begin with a graph of accidents in Chicago between 2001 and 2008:

Clearly there has been a decline in accidents (over 21% between 2001 and 2008). There are a lot of factors affecting accidents from gas prices to the weather. One factor that can be taken into account is how much people drive. The IDOT provides an Annual Vehicle Miles of Travel statistics that allows us to account for how much people drive over a year.

The graphs shows that vehicle miles have dropped in Chicago from 12.6 billion miles in 2002 to 11.6 billion miles in 2008. If people drive fewer miles, it seems reasonable that there will be fewer accidents. We can analyze this by looking at the accident rate for each mile traveled.

This graph shows when we take into account the fewer miles driven in the city, there is no longer a steady drop in accidents. Instead, it’s hard to find a significant trend between 2001 and 2008. It’s also important to note that you can find either a trend of accidents going up, down, or holding steady depending on the what years you include. So once we account for people driving less, there is not a steady trend of accidents dropping.

rshah Chicago, Red Light Cameras