Have you ever been driving along a fairly empty highway only to suddenly find yourself having to slow down for no apparent reason? There's no construction, lane closure, merge, or accident, it's just that suddenly everyone's mysteriously decided to form a traffic jam. After a little while, the problem simply evaporates, though your annoyance usually lingers.

This is what's known as "a phantom traffic jam," and according to new research out of MIT (hat tip to Lifehacker for the pointer), the phenomenon isn't caused by ghosts (or even road conditions). The problem, instead, is tailgaters.

Annoying, unsafe ... and slow

You probably didn't need another reason to dislike tailgaters. Having someone drive nearly close enough to touch your bumper is nerve grating and wildly unsafe, but thanks to science you can now add another item to their long list of sins. Tailgaters aren't just rude and dangerous. They also make traffic worse.

The insight didn't just come out of some professor's loathing of impatient drivers. Instead, it was borne of the Computer Science and Artificial Intelligence Laboratory's work on how best to program the connected cars of the future. While modeling traffic patterns, they stumbled on a truth drivers can put to use today: If we all stopped tailgating like a bunch of jerks, we'd all get where we're going much faster.

Why? By leaving themselves so little space and time to react, tailgaters end up having to slam on their brakes because of even tiny changes in the speed of the car in front of them. This sudden slowdown then forces the driver behind to stomp on her brakes too, then the one behind her, and so on down the line. Each of these cars then needs more time to get back up to speed, and a "phantom" traffic jam is born. (Click here for a nifty animated graphic illustrating the problem.)

"Our work shows that, if drivers all keep an equal distance between the cars on either side of them [front and back], such 'perturbations' would disappear as they travel down a line of traffic, rather than amplify to create a traffic jam," comments MIT professor Berthold Horn.

Horn's team suggests adding sensors to the front and back of cars so that they keep a reasonable distance apart on all sides. That's a nifty solution, but until that technology becomes mainstream we could all just take a lesson from this research and stop tailgating. Then everyone would get where they're going a whole lot faster and a whole lot happier.

Zipcar Co-Founder on the Biggest Questions About Autonomous Vehicles
Published on: Dec 22, 2017