For 15 years, a silent guard has stood watch over the intersection of Neil Street and Bradley Avenue, guiding Champaign cars and pedestrians as they travel through it.
Twenty-four hours a day the guard is responsible for making sure travelers reach their destinations safely and on time.
The guard is actually one of 33 cameras placed atop traffic signals at the busiest intersections in Champaign.
While it might appear positioned to photograph cars running red lights, the cameras have specially designed software to sense the presence of vehicles at intersections. They then use that information to safely trigger signals and conduct the flow of traffic.
The systems cost about $20,000 to buy and install but the maintenance costs are minimal. Each camera requires a lens cleaning only once a year.
Champaign Administration Services Supervisor Kris Koester said the cameras do not have the capability of detecting license plates or filing citations for cars that run red lights.
He said the cameras are solely for the operation of the signals.
“We’re not Chicago,” Koester said in reference to the scandal uncovered by the Chicago Tribune last summer on red light cameras. “There is no recording, moving, or storing of camera images. The resolution is barely good enough to detect a car from a truck.”
Traditionally, traffic signals across the U.S. function in two broad categories – pretimed signals and actuated signals. Pretimed signals are the cheapest and simplest as the lights are programmed to change in predefined intervals. Actuated signals rely on detection equipment to change the signals when activated by a vehicle at the intersection.
The traffic signal cameras in use in Champaign are actuated signals. There is similar video detection equipment in place in Urbana.
However, the most common detector in use in the U.S. is the loop detector, says Dr. Rahim Benekohal, professor of civil engineering at the University of Illinois in Urbana-Champaign. His expertise is in traffic flow modeling. In their most basic forms, loop detectors are loops of wire placed in the surface of the pavement that use a magnetic field to detect cars that pass over them.
While they may be reliable, loop detectors are required to be placed in the pavement surface which has more complex installation and maintenance requirements than other detection methods.
“The newest (detectors) are microwave detectors,” says Benekohal. “The advantage of microwave detection (and video detection) is that you don’t have to dig the pavement.”
Microwave detectors function by emitting a wave across the intersection that bounces back when it comes in contact with a vehicle. Unlike video detectors, microwave detectors are not affected by lighting conditions and therefore function more reliably in rain, fog and at night.
Champaign Traffic and Lighting Operations Supervisor Glen Berger said the city takes into account many factors that play a role when selecting the proper detection equipment to use at intersections.
Along with video detection, loop detection and microwave detection, Champaign also utilizes Sensys “puck” detectors. These are cylinders in the shape of tall hockey pucks that detect changes in the magnetic field, similar to the way loop detectors function.
Urbana relies most heavily on loop detectors; however, there are two intersections with video detectors in place as well as a thermal camera at the intersection of Florida Avenue and Philo Road that is able to detect heat signatures. The intersection at Airport Road and Cunningham Avenue uses both thermal and video detection to actuate the signals. Craig Shonkwiler, assistant city engineer at Urbana, said the thermal camera costs more to implement – about $34,000 – but it allows the detector to sense the presence of bikes and pedestrians as well as vehicles.
Ultimately, says Benekohal, there are two factors at play in designing traffic flow systems in urban environments: making sure the public is safe and that people are able to make it to their destination in a reasonable amount of time.
“There is no single technology about which you can say, ‘This is the best, it’s flawless, it works for everything.’ Every single technology has strengths and weaknesses.”