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Tesla Model S Regenerative Braking and Brake Lights, Intrusive or Responsible?

Tesla Model S Regenerative Braking
Tesla Model S Regenerative Braking

A Tesla Model S tester at Edmunds.com was recently testing the adjustable regenerative braking system and its relationship with the brake lights, bringing up what could be a valid point.

Apparently Senior Editor Jacquot and myself see brake lights in the same way. If you decelerate using your brakes, the brake lights come on as a warning to those behind you that they should be ready to slow down, themselves, to avoid rear-ending you. In town, this makes sense, so no matter what vehicle you drive, whether it be a Tesla Model S or Toyota Prius or Jeep Wrangler, brake lights make others aware of your intentions so they can react accordingly.

Over 55mph, on the highway, brake lights behave in a completely different way. At least, drivers react to brake lights differently. One study I read mentioned that one person lighting up his brakes in steadily flowing traffic can actually affect up to two hundred cars behind him. If you ever have been in flowing highway traffic and then you get to the inchworm stage – race, stop, race, stop – it’s hard to get back to that normal flow. It’s all thanks to that one guy in front who tapped his brakes or cut someone off and made them tap their brakes.

When I’m driving on the highway, even in an automatic, I usually try to downshift just to avoid starting the chain-reaction that leads to inchworm traffic. The Toyota Prius and Tesla Model S employ regenerative braking whenever you let off the accelerator, which mimics conventional-vehicle engine braking, slowing down the vehicle, moderately, without using the brakes. In a Prius, you can leave it in “D” for mild regenerative braking, or put it in “B” for aggressive regenerative braking, but as far as I know, it doesn’t affect the brake lights either way. The Tesla Model S, apparently, has some link between “Standard” and “Low” regenerative braking and the brake lights, which brings up a traffic concern, both to Mr. Jacquot and perhaps others like myself.

In his non-scientific method of observation, Jacquot noted that the brake lights on the Tesla Model S illuminate when letting off the accelerator in standard regenerative braking mode, in spite of the fact that the brake pedal had yet to be applied. In low regenerative braking mode, the braking effect was less aggressive and the brake lights didn’t illuminate until the brake pedal was actually depressed. Should the Tesla Model S have this relationship between regenerative braking and the brake lights, or could the Tesla Model S regenerative braking system be contributing to highway inchworms?

Jacquot suggests that perhaps the rate could be more fine-tuned than it is now, allowing the driver to determine the rate, and I think we both agree that we’d rather see the brake lights linked only to the brake pedal.

Image © Edmunds

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  1. I totally disagree. The regeneration system on the Model S is often the only brake you use, and is quite aggressive at slowing you down VERY quickly. Much more so than the Prius. Therefore, for the safety of those behind you, the brake lights must illuminate.


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