Smart Cameras Blog

Part 1 of this report considered accident trends in Chicago between 2001 and 2008. Part 2 focuses on accidents at traffic signals. This part focuses on accidents at 39 red light camera (RLC) Intersections based on Illinois Department of Transportation (IDOT) data obtained via the Chicago Tribune. The accident data is publicly available here.

The results show that accidents went UP 5% at the intersections with RLCs. This is a shocking result, because you would expect accidents to decline with the introduction of RLCs. The results also stand counter to the general trend of accidents falling at in Chicago about 7% between 2005 to 2008, as well as the 7% drop of accidents at traffic signals.

Results:

The simplest analysis we did was to look at accidents 1 year prior to the startup date and compare it to accidents 1 year after the start up date for the red light cameras. We found a total of 1118 accidents at the 39 intersections 1 year prior to the startup of the RLC. We compared this to 1 year after the startup date and we found a total of 1192 accidents. So in first year the RLCs were used, accidents as a whole went up at the RLC intersections!

We also used a longer time period, which varied according to the data we have for the individual intersection. The longer time period varied from 347 days to 1080 days with a mean of 500 days. This data also found an increase 4.5% in the number of accidents.

We examined the data to see if there was any “bumps” or changes in red light accidents over time. For example, was there an immediate decrease in accidents and then accidents went back up after 3 months? We found that the rate of accidents was constant at intervals of 1, 3, 6, 9, and 12 months.

Unfortunately, we don’t have access to the entire data set (without manually entering in the Tribune data), so we can’t perform a more sophisticated analysis, such as whether there were changes in the types of accidents (angle & rear end) at RLC intersections.

There are two sources of data on accidents at the RLC intersections. The first is from the Illinois Department of Transportation (IDOT), which is used here. The second is from Chicago’s Department of Transportation (CDOT). Accidents at intersections are measured differently by both agencies. CDOT defines the intersection as extending along the arterial street for a distance of 25 to 50 feet while IDOT will use measurements of 150 to 300 feet. Despite the differences in measurements, we believe any tanglible affect of RLCs should be found at either distance.

The startup dates for the cameras varied from January 1, 2006 to Nov 26, 2007. The analysis compares accidents in the year prior to the installation date to one year after the installation, e.g., for a camera installed on April 1, 2006 the year prior data is from March 31, 2005 to March 31, 2006. The year after is April 1, 2006 to April 1, 2007.

rshah Chicago, Red Light Cameras

[From The Associated Press: NJ city leading way in crime-fighting technology]

East Orange, NJ is a city with high crime that has decided to fight crime with new leadership and technology. The question is how much credit is due to the technology. The AP article highlights some of the technologies East Orange is using:

• Database for crime data instead of using paper reports
• Wireless computer system for all patrol cars
• Video surveillance cameras in high-crime areas
• Virtual community patrol system for residents to report crimes via text message
• Grid showing patrol cars’ locations
• Gunshot detection system that tracks the source of shootings.

The article next mentions the next generation smart camera technologies that East Orange is adopting:

The sensors, which work in concert with surveillance cameras, are designed to spot potential crimes by recognizing specific behavior: Someone raising fist at another person, for example, or a car slowing down as it nears a man walking on a deserted street late at night. Each new crime recorded is programmed into the database.

“They know what is normal behavior,” said Tarik Hammadou, whose Australian company, Digisensory Technologies, makes the sensors. “And when there is abnormal behavior like an assault, we annotate it and say to the sensor, ‘This is an assault,’ so the sensor will always remember the pattern.”

When the sensor raises an alert, an officer sitting in the department’s nerve center can zoom in on images to see if a crime is in progress. A computer program sends the information to a laptop in the patrol car nearest to the scene. The whole process takes seconds

As the article notes, the effectiveness of these technologies is questionable.

rshah Other Cities, Vendors

Part 1 of this report considered accident trends in Chicago between 2001 and 2008. This part focuses on accidents at traffic signals. The theory behind red light cameras is that people will drive more carefully at intersections. If they are driving more carefully, we should expect accidents to fall across all traffic intersections, not just the ones with red light cameras.

Here are the main points:

1. Accidents at traffic signals are down, but once we account for the general drop in accidents, the accident rate at traffic signals is holding relatively constant. (There is no halo safety effect from the red light cameras on accidents.)

2. There appears to be a steady drop in Angle crashes over the last 5 years, indicating that there is a change in behavior at traffic signals.

First, consider the overall trend in accidents at traffic signals:

A quick look at this graph shows that it is very similar to the overall drop in accidents. To factor out the general trend of accidents dropping, we next determined the percentage of accidents that occur at traffic signals in Chicago between 2001 and 2008.

This graph shows that the percentage of accidents at traffic signals hasn’t changed appreciably between 2001 and 2008. If people were driving more carefully at traffic signals, it would be expected that accidents at traffic signals would become relatively rarer. For example, dropping from a share of 25% of all accidents to 20% of all accidents. The results here suggest that traffic signal accidents are holding relatively constant. This also suggests the RLCs are not having a halo effect because accidents are not dropping throughout the city at traffic signals.

The next step was to consider the types of accidents occurring at traffic signals in Chicago between 2001 and 2008.

The biggest finding here is the drop in Angle crashes (crashes where cars are heading in different directions). Between 2003 and 2008, there is a 5% drop in Angle crashes at traffic signals. This is a large! This drop supports the argument that red light cameras are leading drivers to be more careful at traffic intersections.

For both turning and rear end type crashes, their was little change with the exception of the 2008 numbers. Hopefully, 2009 numbers will identify if there is a trend in an increased share of rear end accidents and a decreased share of turning accidents at traffic signals.

This data was obtained from the Illinois Department of Transportation (IDOT). IDOT has a separate variable for traffic signals in their accident data.  This allows us to isolate accidents that occur at traffic signals.

rshah Chicago, Red Light Cameras

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

My red light camera study is going public this week, you can see TV coverage over at FOX – New Analysis Shows More Crashes at Intersections With Red Light Cameras.

A longer description can be found at The Expired Meter. I will provide the full report in a few days for everyone.

rshah Chicago, Red Light Cameras