Rules of the Road

Road Rules: Electric car brake lights may work without braking

Dashboard of an earlier model of the Honda Insight, a gas/electric hybrid. Electric car brake lights may come on when the car is slowing, even when you don’t press the brake pedal.
Dashboard of an earlier model of the Honda Insight, a gas/electric hybrid. Electric car brake lights may come on when the car is slowing, even when you don’t press the brake pedal.

Question: I’m seeing more electric cars on the road every day; I myself am the proud owner of one. One of my favorite aspects of driving electric is the regenerative braking, which allows me to slow down without using the brake pedal. Sometimes I am concerned about drivers behind me not paying enough attention to realize I’m slowing down without seeing brake lights. If I’m hit from behind while using regenerative braking, can I be held partially liable because I didn’t engage the brake lights?

Answer: Until you mentioned it, I hadn’t thought about brake lights and regenerative braking, which is one more indicator that I probably shouldn’t be a legal adviser for the National Highway Transportation Safety Administration. By the way, if you ever end up in a room full of traffic safety people, they won’t refer to that organization by its full name or even by saying each initial; they just cram all the initials together into the made-up word, “Nitsa.” It’s much faster, and since NHTSA is connected with just about anything that has to do with traffic safety, saying “Nitsa” instead of the full name throughout a traffic safety professional’s career saves 700 hours worth of unnecessary syllables. That’s just a guess; I don’t have the data to back up that 700 hour claim.

But back to the original question. The folks at NHTSA have given it some thought, and buried in a chart in Title 49 of the Code of Federal Regulations where they specify that stop lamps are required to come on when the brake pedal is engaged, they add that stop lamps “may also be activated by a device designed to retard the motion of the vehicle.” This gives manufactures permission to turn the brake lights on during regenerative braking.

Here’s a bit of trivia to throw out the next time you want to be the life of the party: Even though pretty much everyone uses the term “brake lights,” in legal documents at the state, federal and international level, it’s “stop lamps.” While I can’t find any requirement in a U.S. statute that requires manufacturers to activate stop lamps during regenerative braking, there is an international rule. The United Nations (who knew they were involved in vehicle safety requirements?) has a work group that creates rules to harmonize vehicle safety on a global level. Their code specifies requirements for when stop lamps should illuminate based on deceleration in meters per second when using regenerative braking.

Even though there isn’t a similar requirement in the U.S., in order for vehicle manufacturers to compete globally, they have to comply with the UN’s rule. If you drive an electric car that is sold internationally you most likely have stop lamps that come on when you use regenerative braking and reach the deceleration threshold set by the UN standards. Next time you’re driving at night, check your rear-view mirror when the regenerative braking comes on. You may be able to see your brake lights reflecting off nearby surfaces.

To finally answer your question, I’d say there is a 94 percent chance that if you are involved in a crash, it will be a result of human error rather than the failure of your brake lights to illuminate. At least that’s what the data from NHTSA suggests.

Road Rules is a regular column on road laws, safe driving habits and general police practices. Doug Dahl is the Target Zero Manager for the Whatcom County Traffic Safety Task Force. Target Zero is Washington’s vision to reduce traffic fatalities and serious injuries to zero by 2030. Ask a question.