No left turn for autonomous vehicles?

April 24, 2017

Autonomous vehicles that can flawlessly make left turns are a ways off, according to Hiawatha Bray. “In a perfect world, cars and trucks would never turn left,” he writes in The Boston Globe. Left turns waste time and gas and are dangerous for drivers, oncoming traffic, and crossing pedestrians, he says, adding, “So imagine teaching a machine to turn left—in Boston’s infamous traffic, no less?”

He quotes John Leonard, a professor at MIT who specializes in self-driving vehicles, as saying, “I see a lot of challenges every day, and left turns is near the top of the list.”

“Left turns are so tough because they involve psychology as well as technology,” Bray writes. Drivers and pedestrians read and interpret subtle signals from each other as they approach an intersection.

“Human beings are remarkably good at that, because we’re social beings,” said Gill Pratt, chief executive of the Toyota Research Institute, as quoted by Bray.

Or perhaps not. According to Jim Hyatt writing in Claims Journal, “In 2013, 31% of Arbella Insurance Group’s severe accidents—claims totaling at least $100,000 in bodily injury and property damage—involved a left-turning vehicle.” Presumably, none of the vehicles involved four years ago were autonomous. Hyatt adds, “The U.S. Department of Transportation reports that nationwide, 53.1% of crossing-path crashes involve left turns. Additionally, a study by New York City transportation planners found that left turns were three times as likely to cause a deadly crash involving a pedestrian.”

So maybe we should teach humans to make left turns before worrying about machines making them. Furthermore, there’s a case to be made for banning most left turns altogether. UPS drivers avoid left turns whenever possible in commercial zones.

As CNN reports, “UPS trucks almost never take left-hand turns. By favoring right-hand turns at all times—unless a left is unavoidable—the carrier saves millions of gallons of fuel each year, and avoids emissions equivalent to over 20,000 passenger cars. The practice started decades ago, before computers and GPS, and is now managed by a software that conjures the most efficient route for each truck.”

As far as the safety of left turns goes, autonomous vehicles may have some advantages, even if they are not experts at divining the intentions of pedestrians and human drivers.

Bray in the Globe quotes Tom Vanderbilt, author of the bestselling book Traffic: Why We Drive the Way We Do, as saying, “What makes [the left turn] particularly hard—particularly as we get older—is that we are not very good at judging the speed and distance of objects coming from straight ahead. We only begin to exactly discern the speed and distance of the approaching car when it’s very close to us. Which is often too late.”

In contrast, as Bray acknowledges, autonomous vehicles have no problem judging the speed and distance on an oncoming vehicle. V2V and V2I technologies could further improve autonomous vehicles’ performance.

Waymo seems unperturbed by left-turn challenges. The company received a favorable report on autonomous-vehicle disengagements from California earlier this year.

Dmitri Dolgov, head of Waymo’s self-driving technology, said, “Our report shows a marked improvement in our fully self-driving technology. Since 2015, our rate of safety-related disengages has fallen from 0.8 disengages per thousand miles to 0.2 per thousand miles in 2016.”

Dolgov added that Waymo’s work “…has given us valuable experience sharing the road safely with pedestrians and cyclists, and practicing advanced maneuvers such as making unprotected left turns….”

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