Cars turn left from Bathurst St. to St. Clair Avenue during an advanced green light. Experts say a ban on left turns would help get twice as many cars through an intersection in the same amount of time.The Globe and Mail
Vikash Gayah has a simple way to prevent crashes and reduce traffic snarls – and he knows you won’t like it.
“In downtowns, let’s just get rid of left turns,” said Gayah, a professor of civil engineering at Pennsylvania State University. “I’ve talked to the media about this and I’ve literally gotten hate mail.”
While some cities ban left turns at certain intersections, often only at certain times, a blanket ban in downtown areas would reduce collisions and help drivers get where they’re going faster, Gayah said
That’s because, not only are left turns among the most dangerous manoeuvers you can make on the road (about 60 per cent of all intersection crashes involve left-hand turns), they also take time, he said.
That’s especially true in cities with dedicated turn signals (usually a green arrow) that lets you turn left while oncoming cars have to wait.
While those signals can reduce collisions, they also slow the overall flow of traffic, Gayah said.
“So while it’s much safer, it’s actually pretty inefficient because you’re stopping all other traffic to allow just a few left-turning vehicles to move,” he said.
Those left-turn signals can last for up to 20 seconds, he said.
Plus, at some intersections, after the green arrow ends, there’s often a short period of time where no cars are allowed to move, he said.
“That’s used to clear the intersection. It’s only two to three seconds,” he said. “But that adds up every time you do it. That’s more and more time that the intersection is ... not serving any vehicles.”
That’s where banning left turns entirely comes in. In several papers, Gayah’s team has calculated that a left turn ban could get up to twice as many cars through intersections in the same amount of time.
“It does seem counterintuitive, but it is what we found and verified time and time again, with math and simulations,” he said.
Three rights make a left?
But there’s “a downside,” Gayah said. Because they couldn’t turn left, cars would need to make three right turns to get where they need to go.
“I would have to travel four additional block lengths. That’s the worst-case scenario,” he said. “But what we found is that you’re waiting less time at each [intersection] and you’ll actually [still] get to where you need to go more quickly.”
So if it makes traffic flow better, should left turns just be banned everywhere?
Downtown areas make the most sense for a ban because they usually have short blocks, which means that drivers won’t have to go far out of their way if they’re barred from turning left, he said.
“We’re really focused on the downtowns because in order for this strategy to be viable, you need to have alternative routes,” he said. “In a suburban area or a very rural area, there’s not a lot of [main] roads around. If I can’t make a left turn here, I might have to go miles out of my way in order to find that alternative path.”
Plus, in downtowns, there tend to be more pedestrians and cyclists in a concentrated area.
“When the vehicle is looking to make a left turn, the driver is usually focused on the opposing traffic and they’re not really paying attention all the time to the pedestrians or cyclists,” he said. “So I think it’s a really good strategy in terms of safety and it turns out that it also happens to make things more efficient. So it’s kind of a win-win.”
But, it might make sense to only ban left turns when it’s most congested, he said.
“If it’s [2 a.m.] and you’re sitting at a traffic light and you need to make a left turn, who cares if the intersection is operating at maximum efficiency?” he said. “When it’s not busy, allowing left turns is totally fine.”
While turning an intersection into a roundabout can also improve flow, it requires digging up the intersection – and there might not be enough space for a roundabout in a downtown core where buildings are often close to the sidewalk, Gayah said.
Out of left field?
While banning all left turns in certain areas makes sense on paper, Gayah doesn’t know of any cities that are doing it.
Toronto and Vancouver, for instance, both ban left turns at some intersections. Both said they are not considering a blanket ban.
“Many traffic engineers are familiar with the concept of a blanket left turn ban, however, implementing such a measure requires substantial community support,” Fiona Hughes, a City of Vancouver spokeswoman, said in an e-mail. “Thorough analysis, appropriate infrastructure adjustments and acceptance that vehicle kilometres travelled may increase would be needed.”
Shane Gerard, a City of Toronto spokesman said they look at each intersection individually to avoid “unintended consequences” of across-the-board changes.
Angelo DiCicco, chief executive officer of the Ontario Safety League, a Mississauga-based nonprofit focusing on driver education, thinks there are situations – including traffic jams – where it’s safer and potentially faster for drivers to skip a left turn and make three right turns instead.
While he’s skeptical of a blanket ban, he thinks it’s a good idea to consider limiting left turns at problem intersections.
“It’s worthy of our discussion. We have active monitoring of the traffic flow in intersections with cameras and sensors that we didn’t have five or 10 years ago,” he said. “[Any ban] needs to be data-driven and monitored by traffic engineers.”
DiCicco thinks evidence that left turn bans are easing congestion and preventing crashes could help temper the public outcry.
“You want to get to where you’re going faster rather than slower. That’s why you’re in a car,” he said. “You may not think about it that often, but what you really want is to get there alive and without having to go to the collision-reporting centre.”
If the idea is ever implemented, Gayah hopes that drivers would quickly realize the benefits.
“I don’t know that anyone has a right to a left turn, but if you take it away, people are going to be unhappy,” he said, adding that GPS apps would help drivers in those areas get where they’re going without left turns. “But if they realize that they’re getting to work early or they’re getting home early, I think they would get used to it.”