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How traffic lights might talk to your next car

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The Audi Traffic Light Information system will tell you when a light is about to turn red or stay green. (image: Audi)
The Audi Traffic Light Information system will tell you when a light is about to turn red or stay green. (image: Audi)

On a Monday night in Washington, I easily rolled through an intersection in a new Audi A8. The next traffic light at the end of a block of Pennsylvania Avenue was glowing a steady green. But instead of keeping my foot on the gas, I took it off.

The car told me to do that: This A8’s dashboard reported that the green light would expire before I reached it, then I’d have to wait about 70 seconds. And as forecast, the light turned from green to yellow to red before I would have cleared it.

Nearing other intersections around the District and Northern Virginia, the same display assured me that I would hit the next green, and even told me how fast to drive—usually at the speed limit, but in one case five miles per hour under it.

This vehicular telepathy came from a smart-cities technology that lets traffic lights talk to vehicles. At a minimum, it could lend some tranquility to your drive. At best, it could save fuel and therefore money, and speed everybody’s commute, even for people on the bus.

How traffic lights can talk to a car

The A8 L quattro Audi loaned incorporates what the German carmaker calls Traffic Light Information. Built with Beaverton, Ore.-based Traffic Technology Services,TLI pulls timing data from nearby lights via the car’s AT&T (T) LTE connection and displays that on its dashboard and a heads-up display projected on the windshield.

When launched in the U.S. at the end of 2016, TLI only provided red-light countdowns, but in February Audi added "GLOSA"—a Green Light Optimized Speed Advisory of how fast or slow to drive to meet a green light.

When all this works, it’s like a road superpower. You know the state of a traffic light before you can see it—best case, it will be green for you, worst case you know how long you’ll wait, give or take a few seconds.

(Audi’s system stops counting down with about five seconds to go, a step meant to discourage drag-racing starts.)

Turn-only lanes and signals can confuse this system, though. Its red-light countdown once dropped from about 70 seconds to 7 when the car took a moment to realize I was in a left-turn lane with a separate signal.

The traffic light recognition feature is impressive, but it's not available everywhere. (image: Audi)
The traffic light recognition feature is impressive, but it's not available everywhere. (image: Audi)

But more often, traffic made TLI’s advice not just useless but dangerous: Driving the recommended 35 or 40 mph would have sent the A8 barreling into the back of a bus.

TLI deployments in the District and Virginia also suffered from spotty implementation. I didn’t encounter any intersections online in D.C. Sunday afternoon, and a day later numerous intersections remained offline. In Northern Virginia, I learned that the 1,450-plus signals online did not include such traffic clots as the intersection of Leesburg Pike and International Drive in Tysons Corner.