In some municipalities, the days of seeing flashing lights in your rearview mirror after accidentally running a red light are gone and have been replaced by red light cameras (RLC). Unlike human police officers, these red light cameras work 24 hours a day, 365 days a year, constantly on the lookout for red light violators. Drivers may not even be aware of a violation until they open their mail weeks later. Red light cameras can detect cars running a red light, as well as failure to stop at a right-on-red intersection. Generally speaking, red light and speed cameras are different, though some are able to perform both functions. Both cameras types differ from traffic cameras used to monitor traffic flow.

To get around some legal issues, violations detected by red light cameras are considered non-moving violations and there are no criminal charges associated with them. They are not reported to insurance companies, so it does not matter who the actual driver of the vehicle was. Administratively, they are treated like parking tickets.

History and Usage

Red light camera with speed detection. Source: Gatso USANetherlands-based company Gatso developed the first traffic cameras in the 1960s. Gatso has a long history in the traffic enforcement industry, having created the world’s first speed-measuring device, the Gatsometer. While Gatso secured an early lead in the European market, they are not alone in the manufacture of these cameras. Poltech International supplies Australia, South Africa, Taiwan, the Netherlands, Great Britain and Hong Kong. American Traffic Solutions (ATS) and Redflex Traffic Systems are the primary suppliers to the U.S., and Jenoptik provides cameras to the worldwide market.

Camera usage for traffic law infractions can fall into two categories — speeding and red light violations. According to the Insurance Institute for Highway Safety (IIHS), 22 states plus Washington D.C. use cameras to enforce traffic laws at red light intersections. Fourteen of these states and Washington D.C. use cameras for both speeding and running red lights, seven for red light violations only and New Mexico exclusively for speeding tickets. In these 22 states, 411 communities use cameras for ticketing red light violators and 146 communities for speeding.

The U.K. has been using red light and speed cameras since 1992. Australia, Canada, China, Hong Kong, Singapore, South Africa, Taiwan and many European countries also employ cameras for enforcing traffic laws.

Map of states using traffic law enforcement cameras. Source: IIHS

How Red Light Cameras Work

Red light cameras take still pictures of violators when a car is detected running a red light. Gatso’s first RLC, a film camera introduced in 1965, operated via a series of tubes stretched across the road. Development improvements by Gatso continued over the years and led to the first digital red light camera in 1997.

Digital cameras eliminate the need for film retrieval and allow the cameras to be active around the clock. Many modern cameras are capable of taking video as well as high-resolution still pictures of vehicles as they illegally pass through a red light.

Until recently, different cameras were needed for traffic signal violations and for speeding. New cameras are capable of detecting both and eliminate the need for two separate cameras. Someone who speeds through a red light may be ticketed for both infractions. Most intersections have cameras facing each direction to take pictures as the vehicle approaches and exits the red light.

Cameras are enclosed in a protective, weather-resistant housing and usually mounted on poles. Most jurisdictions require that signs be posted warning motorists that a red light camera is in use.

A couple of different technologies are used to sense vehicles as they approach an intersection with an equipped red light camera.

In-road or over-road sensors detect the presence of a vehicle. While radar and inductive loop are the most common, several types of sensors are in use today.

In-Road Sensors

Inductive loops are the most common type of roadway sensors. An inductive loop is created by embedding wire loops in saw cuts in the pavement. When a conductive metal vehicle passes over it, a change in inductance is detected.

Magnetometers and magnetic detectors placed below the surface detect a change in the magnetic field when a metallic object passes over it. Both magnetic sensor types can also tell if a vehicle is stopped. Vehicles and magnetometers can detect the presence of two vehicles as close together as one foot.

Over-Road Sensors

Radar detection systems use a laser or microwave radar to detect the speed of a vehicle as it approaches a traffic light. When the light turns red the radar detects the speed as the car approaches the limit line. A computer determines whether the speed is slow enough for the vehicle to stop and, if it is, the camera does not photograph the car. If the speed is determined to be too fast for the vehicle to stop in time, the camera takes pictures and, if equipped, a video of the violation. These cameras can also detect speeders, even if the light is green.

Video image processors are located in cameras mounted to poles on the side of the road or on the traffic signal mast arm.

Ultrasonic sensors emit ultrasonic sound waves and detect the presence of a vehicle when they are reflected off of it.

Other sensor types like passive infrared sensors emit and detect infrared radiation, while acoustic sensors are located along the roadside and convert sound waves into electrical energy.

If the light is red and one of the sensors detects a vehicle, the computer in the camera estimates the speed of the vehicle and starts photographing it if the speed exceeds a threshold value.

When a violation has been determined, the following information may be recorded:

• Photographs and video, if equipped
• Date and time of the violation
• Location details of the intersection
• Direction the vehicle was traveling
• Lane the vehicle was driving in
• Speed of the vehicle
• Speed limit where the camera is located

In most cases, the information from the cameras is transmitted to a vendor who reviews the data. When a violation is confirmed, the vendor either sends the information to local law enforcement or issues the ticket on their behalf. The information collected, including photographs, is included in the citation.

The Effectiveness Debate

Red light camera and warning sign in Springfield, Ohio. Source: Derek JensenOne of the main reasons given in support of red light cameras is driver safety. According to a 2009 report by the World Health Organization, 1.03 million motorists are killed annually in traffic accidents and an additional 20 to 50 million suffer non-fatal injuries. A 2013 study by IIHS confirmed the benefits of red light cameras and stated that violations decreased, especially for the most dangerous type of violations that occur 1.5 seconds or more after the light turns red. The study concluded that these cameras contributed to a change in driver behavior and a reduction in violations translated to fewer accidents. A 2016 IIHS study showed that cities experienced a 30% increase in red light running fatalities when cameras were turned off and a 16% increase in fatalities of all types of infractions at intersections with traffic signals. The study further showed that cities with active red lights had 21% fewer red light running fatalities and 14% fewer fatal crashes of all types.

Many GPS and map apps, such as Google maps and the popular Waze app, have integrated red light cameras into their software and warn motorists as they approach an intersection. These apps, combined with warning signs, have increased driver awareness of the presence of red light cameras.

Red light traffic camera locations in Albany, N.Y. Source: Google Maps

As reported earlier on Engineering 360, some studies indicate that red light cameras do not actually prevent car accidents. Instead, the study indicated that once motorists become aware of the cameras they change their behavior and there is a higher incidence of braking hard at yellow lights that leads to more rear-end collisions and minor fender-benders. The National Motorists Association sites numerous articles supporting these findings and sites additional data showing that the number of accidents increases when red light cameras are in use.

According to a recent Fox News story, seven states are currently considering legislation that would make use of red light cameras illegal. Reasons vary from ineffectiveness to constitutional questions and corruption charges. The corruption charges stem from the practice of privatizing enforcement to third-party vendors, some with the authority to issue tickets. A 2016 Arizona case involving a red light camera vendor led to guilty verdicts for bribery and fraud.

Conclusion

New studies will most likely continue to show conflicting data on the merits of red light cameras and the debate will live on. For each new study that shows the safety merits of traffic enforcement cameras, there is another that contradicts those findings. Negative perceptions, corruption and constitutional arguments may end up ultimately deciding the fate of red light cameras.