Home » Why Flashing Brake Lights Are The Cheap Safety Feature You Never Knew You Needed, And Why They’re Banned From The U.S.

Why Flashing Brake Lights Are The Cheap Safety Feature You Never Knew You Needed, And Why They’re Banned From The U.S.


In the beginning, there was the brake lamp, and it did a decent job. Granted, it wasn’t perfect. Trucks, elephants, and people on penny farthings couldn’t really see low-mounted brake lamps, nor was there an extra method of redundancy should low-mounted brake light bulbs burn out. That’s why the National Highway Traffic Safety Administration mandated high-mount stop lamps on cars in 1986 and on light trucks and vans in 1994. There were a few missteps at first, notably the Chevrolet Lumina APV minivan’s center brake light mounted below the main brake lights, but eventually everyone sorted their shit out and the center high-mount stop light was properly implemented on America’s roadways.

But what about different brake lights for different purposes, say a standard illumination for when you’re slowing down and a super bright illumination for when you’re doing a panic stop and don’t want to become a Cadillac DeVille’s new hood ornament? Depending on what you drive, you may already have this rather wonderful feature.

As with many other safety solutions from the three-point seat belt to the crumple zone, emergency stop signals are originally a European phenomenon. The first stability control-dependent emergency stop signals were fairly crude. Heavy braking would get picked up by the stability control, which would send a signal to the lighting control module and illuminate extra bulbs in the tail lamps on Y2K-era BMW E39 5-Series executive cars equipped with the LCM3 lighting module, E46 3-Series compact executive cars, and X5 midsize luxury SUVs. Since then, emergency stop signals have spread to Volvos like the second-generation S80 sedan and Mercedes-Benzes like the mid-2000s S-Class executive barge. I’ll admit, emergency stop signals are one of the little touches I really appreciate on my 3-Series. Call me a spoiled prat, but I don’t see why other cars don’t have this wonderful feature. Here’s a quick visual of how emergency stop signals, or Dynamic Brake Force Display in BMW-speak, work on an E90 3-Series.

E90 emergency stop signal
Photo credit: BMW

Kinda brilliant, right? As with most pieces of technology, emergency stop signals have grown to be much more impressive than they were in the era of Backstreet Boys and American Pie. Mercedes-Benz was the first to market with brake lights that would flash at 3-5 Hz under emergency braking from speeds above 31 mph (50 km/h), a system that has since been mandated across the European Union. While a few aftermarket companies offer flashing brake light modules, specific control parameters that only flash the lights under emergency braking are really where it’s at. Here’s a brief video on the Mercedes system in action.

However, such advancements come with caveats. Because of outdated North American lighting standards, Americans can’t actually have these fancy flashing brake lights. See, FMVSS 108 is the governing document for vehicle lighting in America and section 5.5.10 states that all lamps that aren’t headlamps, turn signals, hazard warning lamps, side marker lamps or school bus warning lamps “shall be wired to be steady-burning.”

In 2005, Mercedes-Benz petitioned the NHTSA to allow up to 5,000 cars with flashing emergency stop signals on American roads, and was firmly denied. It’s rather infuriating to see, considering the evidence in support of flashing emergency stop signals.

One 2014 study found that flashing brake lights reduced the reaction times of participants by 10 to 21 percent given a following distance of two seconds or greater and reduced collisions by 90.9 percent over standard brake lights. Yes, this means that some simple flashing lights could be more effective than automatic emergency braking and wouldn’t require a radar sensor in the grille or cameras in the windscreen. With such an improvement to offer for the low, low price of $free.99, its genuinely maddening that flashing emergency stop signals aren’t allowed in North America.

[Editor’s Note: Part of the issue with flashing brake lights in the US market is that America remains the lone global holdout for allowing red rear turn indicators. The issue with flashing brake lamps is that in the US, they could be mistaken for turn indicators or hazard lamps, a problem that doesn’t exist in the rest of the world where indicators are amber. Sure, we Americans came up with the transistor and the Hot Pocket, but we can be idiots, too. – JT]

Fortunately, intrepid owners of certain late-model cars who value the safety of flashing emergency stop signals over legality aren’t completely out of luck. It’s entirely possible to code flashing emergency stop signals into a late-model Audi, BMW, Volkswagen or Mercedes-Benz, with a variety of forum posts detailing the coding for each model. Yeehaw, fuck the law, am I right? Hopefully the tortoises behind American tail lamp legislation can eventually right this wrong and bring the wonderful lighting innovation to the masses. One can only dream.

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71 Responses

  1. My 2012 Audi will automatically kick on the hazard lights if I panic-brake, though I don’t believe it is a factory option on North American cars. I have always had the habit of switching on my hazards when I see traffic ahead on the freeway or am braking harder than normal.

  2. Re: BMW E90 3-Series brake light behavior — “. . . as long as the rear fog light is not switched on.”
    Er . . . “rear fog light”? Wha?!?!
    (I need to get out more often!)

    1. Mostly a European thing – cars will have an extra set of the taillamps that don’t normally illuminate, but can be switched on manually when driving in adverse conditions. On my Audi, they are in the middle of the light and come on at full brake light brightness.

  3. I don’t know about other parts of the country, but I see these all the time in Chicagoland. I’ve never considered them particularly useful, it seems like they’re only on the most annoying vehicles on the road

  4. I’m genuinely shocked at those claimed crash reduction numbers.I can’t immediately think how the stats could be wrong.
    It all sounds pretty awesome

  5. I agree that a brake light that flashes on a hard stop is likely useful, especially once the majority of drivers become aware of the feature and understand what they’re seeing when it happens. However, the aftermarket kits that flash the brake lights at the slightest touch are annoying and potentially dangerous.

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