Beware tailgating a BMW i3

The electric car can decelerate without turning on the brake lights

Published: October 10, 2014 02:30 PM

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The moment you lift your foot off the accelerator, the BMW i3 slows down appreciably. It feels like applying the brakes moderately in a normal car. But unless you pretty much lift your foot completely off the pedal, the i3's brake lights don't come on. We think they should. (Read our BMW i3 first drive.)

Despite this surprising behavior, the BMW complies with the law, since the U.S. government has no standard regarding deceleration level for activating brake lights. The German TÜV (a technical safety association) standard dictates a .3 g threshold. BMW says that a deceleration level of .13 g will activate the brake lights; our test equipment confirmed that. But if you slow down the i3 gradually by coming off the gas pedal in small increments, you could come to a complete stop without giving motorists behind you any warning. If the driver following is inattentive in real-world stop-and-go traffic, the lack of red lights in his/her peripheral vision can potentially lead to the i3 being rear ended.

To a lesser degree, of course, a similar situation could arise if you downshifted any car into a lower gear, but the deceleration would typically not be as great as the i3 permits.

BMW's spokesman, Matthew Russell, said that by choosing this brake light activating tactic, the company was trying to avoid frequent brake lights going off due to concern that it would contribute to traffic congestion. Russell said that the company was receptive to our feedback and always looking for opportunities to improve the product.

As with another issue we presented to BMW, regarding the i3 losing acceleration power at inopportune times without warning, we hope a remedy can be made to improve driver safety.

—Gabe Shenhar