Smart Cameras Blog

[From 10 facts about red-light cameras -- chicagotribune.com]

Here is a summary of how the red light cameras operate in Chicago. This material was compiled from a number of sources. The vendors for Chicago’s cameras are RedSpeed Illinois and Redflex Traffic Systems.

The system operates by using “magnetic sensors installed at various points leading up to the stop line to determine whether the camera should begin taking pictures and video. (Video clips are about 12 seconds.) There are no sensors past the stop line, meaning if you’re in the middle of the intersection—waiting to turn left—and the light turns red, the camera should not record the incident. The average intersection has two cameras, although the number ranges from one to four.” (from Tribune).

This technology is also known as loop detectors. Once triggered the cameras take 3 images and 12 seconds of video of each violation. A violation occurs when a vehicle enters an intersection 1/10 of a second after the light has changed to red. The only two legitimate reasons for disobeying a red light are participating in a funeral precession or yielding to an emergency vehicle.

Loop detection technology was chosen, even though its more expensive, because the city felt video detection is not yet mature and has a high failure rate. The cameras are are fixed so they cannot be remotely maneuvered.

A bit more detail can be found at the web site for RedSpeed Illinois. Their explanation is:

The state of traffic signals is continuously monitored and their ‘on’ time recorded by the system. When the red aspect is detected, a timer is started. When this timer exceeds the programmed ‘time into red’, the two road loops are monitored for detection of a moving vehicle. If a vehicle is detected, the program proceeds to violation capture, then two wide-angle images and one zoom image of the vehicle are recorded.

However, the next generation system is known as RedSpeed. Here is what it can do:

The system detects speed violations during the green and amber phases, and also detects red light violations. Three images and a 12 second video clip are captured. The first is a zoom shot showing the vehicle number plate. The second is a wide angle image including the make, model, and colour of car and the offence data. The system then delays, for a period related to the vehicle’s speed, and captures a third frame, also a wide angle image showing the time delay between frames. The two wide-angle images can be used as evidence to show that the vehicle was moving at the time of the recording. (My emphasis)

I would not be surprised to see the RedSpeed cameras deployed next. We will hear how speeding through intersections causes many accidents and how it is necessary to use cameras to deter this behavior. This new technology can save lives and raise money for cities. (They can also be used to gather lots of data on us, see here and here.)

rshah Chicago, Red Light Cameras