The Evolution Of Car Brake Light Laws

The requirement for cars to have two brake lights was superseded in the 1980s when, in 1986, all new cars were legally required to have three brake lights. This was extended to light trucks in 1994.

The Center High Mounted Stop Lamp (CHMSL) became law in 1986 for cars

The Center High Mounted Stop Lamp (CHMSL) became a legal requirement in 1986 for new cars. This law was later extended to light trucks in 1994. The CHMSL, or the third brake light, is an essential safety feature that significantly reduces the risk of rear-end collisions.

The story of the CHMSL's origins can be traced back to a San Francisco cab driver who, after being rear-ended multiple times, took matters into his own hands and installed an extra brake light in his rear window. This innovative solution caught the attention of psychologist John Voevodsky, who, in 1974, conducted a study to test the effectiveness of a third brake light. Voevodsky installed an extra light in the rear window of 343 taxi cabs in San Francisco and found that those with the third brake light had a 60% reduction in rear-end collisions compared to those without.

While larger studies by the National Highway Traffic Safety Administration didn't yield as significant results, they consistently showed that the CHMSL reduced collisions. As a result, the CHMSL became mandatory equipment on new cars sold after September 1, 1985, and light trucks after September 1, 1993. This requirement is stipulated in the RCW 46.37.070(3) statute.

It is important to note that a non-functioning CHMSL is considered a violation of the law. Therefore, vehicle owners are encouraged to fix any malfunctioning CHMSLs to reduce the chance of a rear-end collision and ensure compliance with legal requirements.

In 1994, the CHMSL became law for light trucks

In 1994, the Center High Mounted Stop Lamp (CHMSL) became a legal requirement for light trucks. This third brake light is mandated to display a red light when the brakes are applied. The CHMSL is an important safety feature, as it has been proven to reduce collisions. In fact, a study by psychologist John Voevodsky in 1974 found that taxis equipped with a third brake light had 60% fewer rear-end collisions than those without one.

The CHMSL was first made mandatory for new cars in 1986, and this law was extended to include light trucks in 1994. This law applies to all passenger trucks, as well as passenger vans and SUVs, that were manufactured after September 1, 1993.

It is worth noting that not all vehicles are required to have a middle brake light or third tail light. However, for those that do have one, a non-functioning CHMSL is a violation of the law. Therefore, it is important to ensure that all brake lights, including the CHMSL, are in proper working condition to reduce the risk of a rear-end collision.

The CHMSL is a valuable addition to the lighting equipment of light trucks, enhancing safety on the roads and potentially saving lives.

The CHMSL must be placed at a certain height and centred laterally on the vehicle

The Center High Mounted Stop Lamp (CHMSL) is required to be placed at a certain height and centred laterally on the vehicle. This positioning is mandated by law and is designed to optimise the visibility of the third brake light to other drivers.

The CHMSL is required to be mounted higher than the vehicle's left and right stop lights. The height of the CHMSL is regulated, with specifications dictating its placement in absolute terms and in relation to the mounting height of the vehicle's conventional left and right stop lights. Depending on the height of the left and right lights, the lower edge of the CHMSL may be just above the left and right lights' upper edge.

The CHMSL is also required to be centred laterally on the vehicle. While it should be centred, UN Regulation 48 permits a lateral offset of up to 15 cm if the vehicle's centre does not align with a fixed body panel. This exception accounts for vehicles with movable components such as doors that separate the left and right sides.

The placement of the CHMSL is designed to ensure that it is easily visible to other drivers, providing an effective warning signal when the brakes are applied. This positioning also helps to disambiguate the brake lights from other lighting functions, such as rear position lights and turn signal lights.

The CHMSL is a cost-effective collision avoidance feature that has been shown to reduce the risk of a vehicle being involved in a chain collision or a middle vehicle collision. Its placement at a certain height and centred laterally on the vehicle is an important factor in its effectiveness, ensuring that it can be seen by surrounding drivers and reducing the likelihood of rear-end collisions.

The CHMSL must display a red light when the brakes are applied

The Center High Mounted Stop Lamp (CHMSL) is a safety feature that has been required on all new cars in the United States and Canada since 1986 and on light trucks since 1994. The CHMSL is a third brake light that is mounted higher than the vehicle's left and right brake lights, providing a warning to drivers whose view of the lower lights is blocked. This additional light has been proven to reduce rear-end collisions and improve safety for all motorists.

The requirement for the CHMSL to display a red light when the brakes are applied is part of the larger set of regulations governing vehicle lighting and signaling devices. These regulations specify the colour, intensity, mounting location, and function of various lights on a vehicle. The CHMSL, for example, must be centred laterally on the vehicle and mounted at a specific height in relation to the left and right brake lights.

The addition of the CHMSL as a required lighting feature on new vehicles was the result of research conducted by psychologist John Voevodsky in 1974. Voevodsky's study found that a third brake light reduced the number of rear-end collisions and improved safety for taxi drivers in San Francisco. This research was further supported by larger-scale studies conducted by the National Highway Traffic Safety Administration (NHTSA), which led to the requirement for the CHMSL on all new cars and light trucks.

The CHMSL is an important safety feature that has helped to reduce accidents and improve visibility on the road. By displaying a red light when the brakes are applied, the CHMSL provides a clear and consistent signal to following drivers, contributing to safer driving conditions for all motorists.

The CHMSL may be placed above the back glass or affixed to the interior of the car

The Center High Mounted Stop Lamp (CHMSL) is a third brake light that was made mandatory for new cars in 1986 and for light trucks in 1994. The CHMSL is placed at the center of the rear of a vehicle, at a position as high as is practical. Typically, the CHMSL is placed above the back glass, at the roofline, behind the rear window, or on the trailing edge of the vehicle's roof.

For passenger cars, the CHMSL is usually affixed to the vehicle's interior just inside the back glass or integrated into the vehicle's deck lid or into a spoiler. The CHMSL may also be integrated into a stalk fixed to the spare wheel carrier, as is the case for the Jeep Wrangler and Land Rover Freelander.

The CHMSL is intended to warn drivers whose view of the vehicle's left and right stop lights is obstructed by interceding vehicles. It also acts as a redundant stop light signal in the event of a brake light failure.

The CHMSL is typically a linear light bar comprising a small set of mid-power red LEDs. The light emitted by the LEDs is regulated by some combination of reflective and lenticular optics, which helps create the required far-field intensity distribution. The LED module of a CHMSL is driven by a constant current source.

The use of LEDs as the light source for the CHMSL provides a compelling safety benefit due to the nearly instantaneous response of LEDs to applied electrical power. The instant-on response provided by LED lights reduces reaction time and gains valuable meters of braking distance, giving the operator of the following vehicle more time to execute evasive action.

LED stop lights are also more reliable than filament lamps due to their excellent resistance to constant switching and ability to withstand greater levels of vibration.

Frequently asked questions