- A Gaping Hole In American Safety Law
- Engine Braking Vs. Regenerative Braking
- Hyundai, Kia, And The NHTSA Aware Of The Problem
- The Mercedes Issue
- Immediate Action Required
And it's got nothing to do with the fire risks associated with EV batteries.
Electric vehicles are known for their impressive safety, but they have a significant flaw that the US government has done nothing to stop: regenerative braking systems (RBS) do not automatically activate the brake lights in some cases, and nor are they required to do so by the NHTSA. Worse still, while these vehicles have specific requirements on this matter for Europe, where the lights activate at a certain rate of deceleration, many manufacturers' EVs in the US are simply not activating the brake lights at all, capable of coming to a halt without ever indicating deceleration to cars behind them.
Consumer Reports (CR) has released findings from a new study that claims some electric vehicles do not illuminate their brake lights when decelerating during one-pedal driving.
The organization evaluated several EVs in its fleet, with cars including the Hyundai Ioniq 5, Genesis Electrified GV70, and Kia EV6 not providing other drivers with a sufficient warning – unless the driver removes their foot from the throttle entirely. The Hyundai Group wasn't alone, however, as CR also found issues with Mercedes EVs.
“It's very difficult to judge how rapidly a vehicle ahead is slowing down without the visual cue of their brake lights,” said Jennifer Stockburger, director of operations at the Consumer Reports Auto Test Center. “The lack of that visual aid from some EVs could lead to potentially dangerous situations in which other cars fail to maintain a consistent following gap.”
Consumer Reports tested 24 vehicles (all purchased by the organization) to see how different vehicles would fair in this situation. Engineers measured the speed at which each vehicle slowed down when using the one-pedal regenerative-braking modes, and then monitored at what rate of deceleration the brake lights were illuminated.
While most brake lights came on “appropriately” during strong regenerative braking, some cars failed to use their brake lights – even under “aggressive” deceleration. These include the Ioniq 5 SEL AWD, Genesis GV60 Advanced and Electrified GV70, the Kia EV6 Wind AWD, and Niro EV Wind.
A Gaping Hole In American Safety Law
“On average, we found that the brake lights of most EVs in our fleet illuminate when the regenerative braking system is slowing the car at about 0.1g, which could be described as a slight but noticeable amount of braking force,” added Alex Knizek, CR's manager of auto testing and insights.
Interestingly, the 2023 Hyundai Ioniq 6 in the fleet did not exhibit this problem.
CarBuzz did some investigating and found the US government's legislation on this matter surprisingly vague. Federal Motor Vehicle Safety Standard (FMVSS) No. 108, which covers vehicle lighting, including stop lamps, stipulates that stop lamps “Must be activated upon application of the service brakes.” However, the NHTSA defines the service brakes as “the primary mechanism designed to stop a motor vehicle.”
While you might argue that the RBS forms part of the service brakes, as it automatically actives when you press the brake pedal, the NHTSA told CarBuzz that RBS is only part of the service brake system if “it is automatically activated by an application of the service brake control, if there is no means provided for the driver to disconnect or otherwise deactivate it, and if it is activated in all transmission positions, including neutral.”
Because brake regeneration is not active in neutral, however, it does not form part of the service brakes. FMVSS No. 108 does cover stop lamp activation under the wording “May also be activated by a device designed to retard the motion of the vehicle,” but the word 'may' is important here as there is no legal requirement.
In Europe, regulations require electric vehicles to illuminate their brake lamps every time the regen system's deceleration rate surpasses 1.3 m/s2 or 0.13g. But the NHTSA confirmed to CarBuzz that US legislation “does not require the lamps to be activated at a specific level of deceleration.”
Engine Braking Vs. Regenerative Braking
The same could be said of traditional internal combustion engine (ICE) cars, as when you downshift, an element of engine braking can slow a vehicle without activating the stop lamps. But engine braking cannot slow a car as rapidly as brake regen from an electric motor, and one-pedal driving is not something ICE cars are capable of.
Comparatively, EVs don't even need friction brakes, as the electric motors can apply not only resistance but negative torque to the wheels to slow down as quickly, if not quicker, than friction brakes. Volkswagen knows this, which is why it doesn't bother with complex disc brakes on the rear of the single-motor ID.4, using drum brakes on the rear axle where the rear-mounted electric motor provides most of the brake force.
Hyundai, Kia, And The NHTSA Aware Of The Problem
Hyundai and Kia representatives confirmed to Consumer Reports that the companies are aware of the concerns and that Hyundai Motor Group (HMG) engineers are “looking into the matter,” but that all HMG vehicles meet FMVSS No. 108 standards.
The NHTSA is also aware of the matter but confirmed in a statement to CarBuzz that there are no open rulemakings looking to establish new requirements with regards to stop lamp activation.
“The agency will be discussing these stop lamp issues with the respective manufacturers during their regularly scheduled meetings with NHTSA. NHTSA currently does not have any open rulemakings to establish a new requirement on this topic.”
The Mercedes Issue
In CR testing, four Mercedes-Benz EVs were found to have another potential safety problem. With the strongest one-pedal driving setup in use, the brake lights of the vehicles would turn off when the car came to a full stop, disengaging in some instances when the speed dropped below 5 mph. When the driver takes their foot off the accelerator, the brake lights illuminate when deceleration is around the 0.15g mark.
The brake lights turn off and only return after 15 seconds or so, but CR believes the brake lights should stay on while the vehicle is stationary. The argument could be made here that when you are stationary at an intersection in an ICE car, some drivers engage the parking brake, and some cars with hill hold assist do the same. These do not activate the brake lights so why should an EV? But if we're trying to make vehicles safer across the board, then the automatic activation of these lights should be constant across the board.
Immediate Action Required
Sometimes, following the law to the letter isn't enough. Automakers need to look at the thread of logic behind the creation of the law, which in this case is simple: Why do brake lights exist? To warn drivers behind you that you are actively slowing down a vehicle. Regenerative braking systems serve the exact same purpose, and coming off the throttle (accelerator is a poor term for a pedal that works to both accelerate and decelerate a vehicle) in a high-regen mode actively slows a vehicle, sometimes to a complete stop and more aggressively than light friction braking.
By this logic, drivers behind you should be alerted to your intentions.
The OEMs are ultimately responsible, and the NHTSA's statement to CarBuzz explicitly stated that “NHTSA does not 'approve' or test vehicles prior to their introduction. Manufacturers are responsible for ensuring that their vehicles meet all NHTSA safety standards and must certify the compliance of their vehicles.”
But it is the NHTSA's responsibility “to investigate potential safety issues, and act when we find evidence of noncompliance or an unreasonable risk to safety,” and in this instance, we feel there is a risk to the safety of other road users.
With EVs growing in number daily, the time is now to set the groundwork by which these vehicles are developed. Prevention, after all, is better than cure. What are we waiting for?
Keyword: There's A MASSIVE Safety Flaw With American EV Laws