Here's Why Tailgating at the Light Won't Get You Through Any Faster

Ugh, rush hour. You're stuck at yet another red light behind a line of cars so long that you probably won't make it through once the light changes. If you're like many people, you probably creep closer to the car ahead of you to try and scrape by in the nick of time. But according to science, that won't help. Whether you're two centimeters or two car lengths from the car ahead of you, it'll take you just as long to get through.

Red Light Green Light

Everyone knows that tailgating is dangerous. But when it comes to stopping at an intersection, it makes some sense. If you were standing in line at a coffee shop, for instance, you'd scoot up close to the person in front of you — it's the polite thing to do for everyone behind you. Why wouldn't you do the same in your car?

But tailgating at intersections causes plenty of fender benders, so researchers from Virginia Tech and Duke University wanted to make sure it was worth it. For a study published in the Journal of Physics in November 2017, they had volunteer drivers line up 10 Chevy Impalas at a red light on a test road, sitting at varying distances from each other over a series of experiments. When the light turned green, they accelerated in a "normal and comfortable fashion" while a drone monitored their speed. Easy.

Step Back, You're Drivin' Kinda Close

When the researchers analyzed their footage, they found something surprising: Cars that tailgated took just as long to get through the light as cars stopped up to 7.6 meters (25 feet) back. That's nearly two car lengths. What's going on?

According to the study, it's a little bit like melting ice. Ice can stay frozen for a while before it starts melting because the process of going from frozen to liquid takes a little bit of extra energy known as "latent heat." Likewise, it takes some time for a car to accelerate from a full stop — or, as the researchers write, "the 'temperature' (kinetic energy) of the vehicles cannot increase until the traffic 'melts' into the liquid phase."

In practical terms, that means that the time a tailgating driver has to wait until it's safe to hit the gas offsets the extra space a non-tailgating driver gives the car ahead since that driver can accelerate faster. But don't change your coffee line habits. The team did the same experiment for people standing in line, and in that case, packing closer together gets everyone through faster.

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For more driving science, check out "Traffic: Why We Drive the Way We Do" by Tom Vanderbilt. The audiobook is free with a trial of Audible. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

Written by Ashley Hamer January 25, 2018

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