In 2004, UPS adjusted delivery routes to eliminate left-hand turns to cut travel times, fuel consumption, and carbon emissions. Even though this appears to be a little modification, the outcomes are anything but: UPS argues that eliminating left turns—specifically, the time drivers wait to cut across traffic—saves 10 million gallons of fuel, 20,000 tonnes of CO2, and allows them to deliver 350,000 more items every year.
Should cities aim to prohibit left-hand turns at junctions as well, if UPS has found it to be so successful? According to my study, the answer is a resounding yes.
For nearly a decade, I’ve studied traffic flow on city streets and transportation safety as a transportation engineering professor at Penn State. Part of my profession involves figuring out how to organize and manage city streets. It turns out that banning left turns at intersections with traffic lights improves traffic flow and makes the public safer. My research group and I devised a method to evaluate which crossings should prohibit left turns to improve traffic flow in a recent study.
What is it about left-hand turns that makes them so dangerous?
Intersections are dangerous because they are where cars must cross paths, typically at high speeds and in opposing directions. Meetings account for over 40% of all crashes, with 50% of major injuries and 20% fatalities. Traffic signals make things safer by informing drivers when they are allowed to move. If there were no left turns, the instructions could be quite simple: a north-south route may move while it stopped the east-west route and vice versa. When making a left turn, automobiles must cross oncoming traffic, making crossings significantly more difficult.
Allowing vehicles to wait until a space in oncoming traffic appears is one technique to allow left turns. However, that can be perilous because it depends on the driver to make a safe left turn. And we all know how aggravating it is to be delayed behind a car waiting to turn left on a busy road.
Stopping incoming traffic and giving automobiles turning left their green arrow is another approach to allow left-hand turns. That is substantially safer and closes the entire intersection to allow left-turning vehicles to pass, significantly slowing traffic.
In any instance, making a left turn is risky. A left-hand turn is involved in approximately 61 percent of all intersection crashes.
What are the benefits of removing left turns in terms of traffic flow?
Traffic researchers have recommended several new signal techniques and complex intersection arrangements to make left turns safer and more efficient. However, a more straightforward solution can be preferable: At intersections, limit left-hand turns.
To improve safety and traffic flow. Some cities have already begun banning left turns. San Francisco, Salt Lake City, Birmingham, Alabama, Wilmington, Delaware, Tuscon, Arizona, and dozens of other cities in the United States and worldwide all restrict left turns in some fashion. It’s usually done in remote areas to solve unique traffic and safety issues.
There is, of course, a disadvantage. Some vehicles would have to travel long distances if it eliminated left turns. If you wanted to turn left off a busy route to go to your house, for example, you could have to make three right turns in a row. However, research I presented in 2012 using mathematical models and in 2017 using traffic simulations revealed that eliminating left turns on grid-like street networks will result in individuals driving only one extra block on average. The smoother traffic flow would more than compensate for this.
Which of the left turns should be eliminated?
It would be challenging to eliminate left turns across an entire city, yet left turns do not cause problems at some crossroads. But, if a city wanted to stop left turns at some junctions, how would it decide which ones to eliminate? To answer this question, my research group and I have created algorithms that use city traffic simulations to determine where banning left turns will have the most impact on safety and traffic flow.
The exact answer varies for each city, depending on how streets setting out, where vehicles come from and go to, and how much traffic is on the road during peak hours. However, our models show that left-turn limits are more successful at busier crossings in town or city centres than at less busy intersections further out from the town centre.
That is because the more individuals who benefit from smoother traffic flow, the busier the crossroads become. Alternative routes tend to be available at these major crossings, minimizing any additional distance driven due to the limitations. Finally, because fewer automobiles turn left at these central crossings, the negative impact of eliminating left turns is minor.
So, the next time you trap in traffic behind someone making a left turn, know that your annoyance is well-founded. There is a better way to do things. In this situation, the solution is straightforward: eliminate the left turn.