Before Center High Mounted Stop Lights (CHMSL) were mandated in 1986 for all cars and later in 1994 for trucks, extensive research had been conducted. A psychologist named John Voevodsky executed an experiment on 384 taxi cabs in San Francisco in which he installed a third brake light. After 10 months, he determined the addition of the third brake light resulted in 60.6% fewer rear end collisions.
The National Highway and Traffic Safety Association (NHTSA) further researched Voevodsky’s findings and found that CHMSL were indeed effective in the reduction of rear end collisions. Once it was required that all vehicles have a Center High Mounted Stop Light (CHMSL), no one refuted the evidence and considered it a cost-efficient way to prevent accidents. All cars manufactured after 1991 in the United States are made with a third brake light. After the CHMSL had been used for a number of years, the NHTSA conducted a study in 1998 that showed a significant reduction of 8.5% in rear impact crashes in 1987, that eventually leveled off to a reduction of 4.3% in subsequent years through 1995.
The addition of the CHMSL was shown to be most effective in the day-time, in areas where there are few or no traffic signals, and against two-car collisions occurring at lower speeds, where the driver has ample time to slow down and avoid a crash. It is thought to be less effective at night and at higher speeds when there is much less reaction time. Nevertheless, the report showed the addition of a CHMSL reduces rear impact crashes, saving hundreds of thousands of people from injuries and property damage.
The use of CHMSL is widely accepted, even growing globally. A 2017 report from Research and Markets describes the CHMSL as essential and predicts the High Mount Stop Lamp will grow globally at a CGAR of 4.38% through 2021.
Today, measures to improve automobile and driving safety are a priority. After CHMSL was proven effective, improvements were made to make it better. For example, replacing the previously used incandescent bulb with a Light Emitting Diode (LED) light, enhances the already effective safety measure by reducing brake reaction times. A series of tests conducted by the University of Michigan Transportation Institute (UMTRI) showed how the faster illuminating LED light decreased brake response time by 200 milliseconds, which equates to an additional 19-mile buffer.
In 2014, another study was conducted by the NHTSA to decipher whether the use of Light Emitting Diode (LED) lamps increased the efficacy of CHMSLs. While the study showed significant reduction in rear impact crashes with some models, notably the 2006 Honda Accord, further analysis concluded that rear impact crashes increased when multiple variables and parameters were introduced.
Other improvements to the CHMSL are the addition of a rear camera in some cases, and pulsing lights to indicate hard breaking. A 2014 publication by the University of Michigan features a study that indicates flashing CHMSL at 3 to 5 hertz can reduce brake response times by up to 30%.
Opinions On The Continued Efficacy of CHMSL
An article published by the Chicago Tribune in 2016 questioned if drivers are safer thirty years after the CHMSL mandate. At the time, rear end crashes accounted for more than 40% of vehicular collisions in the United States. The article reported a slight increase in collision related fatalities between 1988, the year after the CHMSL was mandated, though 2014. Additionally, rear end accidents and property damage increased at least 5% during the same time frame. It was noted however, that accidents where speed was the contributing factor had declined since 2009 and other factors such as drug impairment and distracted driving was on the rise. Improved economy and lower gas rates were additional factors thought to add to the rising collision incidents since these elements put more drivers on the road.
An article on an online automotive blog site called A Car Place sites a couple of studies done in 2008 and 2009 by the NHTSA that show the use of amber lights for turn signals as an effective safety feature. The author favors amber lights over red ones and suggests that elimination of the latter would be best for safety. He highlighted a statistic that the use of amber lights are 1% more effective than CHMSL in reducing car accidents. Readers commenting on the blog post didn’t mention CHMSL specifically, but had varying opinions on the use of the color red for rear/tail lighting as opposed to those that are amber colored.
Social Media Analysis
A question was posed in a 2006 forum discussion on a website called Team BHP on whether the use of CHMSL was useful in India (where CHMSL was not mandated). The original poster thought standard brake lights and safe driving was sufficient. The firm response in the thread was that CHMSL was indeed useful as a safety measure.
A 2019 blog post by Napa reinforces the need for a CHMSL to communicate with drivers and add a net of safety (in addition to other rear lights) when braking. The post says that after thirty years, while it is difficult to determine the overall effectiveness, anything that improves visibility is of benefit. It also mentions the blinking feature of some CHMSL can indicate panic breaking. A number of social posts suggest that the blinking/flashing/pulsating feature of some CHMSL are distracting and/or annoying.
In a 2016 blog post on a website called The Truth About Cars, the author describes his disapproval of “flashing” CHMSL lights. The readers commented on whether flashing CHMSL was legal and if it posed any problems. Most of the comments were in agreement that flashing lights are distracting, while a few people thought they would be of benefit to catch the attention of distracted drivers. Others expressed their desire for vehicles to have amber colored tail lights and considered it a better safety feature.
In a Ford Fusion forum, posts from 2019 showed continued frustration with flashing CHMSLs with the overall consensus that they are distracting.
The Gadgeteer advertised the “Braking Bar” in February 2020 as an added safety feature to alert distracted drivers with a pulsating LED light during hard braking. Those commenting pointed out that the pulsating or flashing LED lights would be annoying on this device just as they have seen on flashing CHMSL. Some comments stressed a necessity to be annoying to catch the attention of drivers who would otherwise rear end them.
Aside from the initial research conducted by the NHTSA on the effectiveness of CHML, there were no recent studies found to show its continued effects. Throughout our research, we focused our efforts on finding current studies and opinions concerning the use of CHMSL via industry journals and reports, automotive blog posts, and various social media channels. The information available relied heavily on the NHTSA data. Innovations in automobile and driver safety have built upon the safety of CHMSL and continually add a range of new advancements. The use of CHMSL is widely accepted as essential and the general opinion doesn’t appear to have shifted over time.