Pittsburgh developed from a hodgepodge of former boroughs and municipalities, and its hills and river valleys prevented planners from creating a traditional street grid. These factors make the city difficult to navigate in a vehicle. On top of that, local drivers have some idiosyncratic behaviors.
One of those behaviors is the Pittsburgh Left, which occurs when a left-turning driver turns before the straight, oncoming traffic. The action is applauded by some as alleviating traffic, and criticized by others for being dangerous.
Good Question! askers had a lot of thoughts and inquiries about the practice.
The so-called Pittsburgh Left occurs when two drivers meet at an intersection and there is not a left turn lane or arrow. One driver is going straight and the other has indicated they would like to turn left. The driver going straight allows the left-turning driver to go ahead of him in order to alleviate traffic that may have built up behind the left-turning driver. This is typically indicated by a wave or a quick flash of headlights.
When it began and why
On June 10, 1985, Pittsburgh Post-Gazette columnist Peter Leo wrote a piece called “Right of way left to change,” in which he condemns the Pittsburgh Left. He describes the “Pushy Pittsburgh Left” and goes on to say he remembers the giving of the left to be “out of kindness or a sense of the common good.” But his criticism comes when the left-turning driver takes the action without consent from the straight-lane driver.
“[The Pittsburgh Left] is so commonplace that we stand out in this, according to the testimony of befuddled newcomers,” the article says. “We may be forced to share right-on-red with the rest of the country. But we’re No. 1 when it comes to the pushy left-on-green.”
Leo does mention the main merit of the left: it “keeps traffic moving on a narrow road.” But in his column, he’s very clear that the practice has been happening for quite a while in Pittsburgh.
Alexander Stevanovic, a civil and environmental engineering professor at the University of Pittsburgh, said as cars became more ubiquitous throughout the 20th century, dense city streets weren’t prepared for the increase in traffic.
“When you don’t have enough capacity, that’s when people are going to have to find their own ways to maximally utilize what they have,” Stevanovic said.
After all, Pittsburgh is an older city without a traditional grid system. Its urban layout is a product of small boroughs and communities gradually being annexed into Pittsburgh. A neighborhood like Allentown, which was annexed by the city in 1872, has a grid system within the community (despite the hilly topography). Many other Pittsburgh neighborhoods have similar internal infrastructure that, in some ways, create a new character for visitors as they travel between different places. But it can also make the city feel disjointed.
Mark Magalotti, a professor of practice at Pitt’s Department of Civil and Environmental Engineering, said a behavior similar to the Pittsburgh left may occur in other older cities, like Boston or New York, where there are narrow streets and fewer left arrows.
“But if you go to the Midwest and West where the cities are much newer, where the boulevards are widers, streets were designed for left turn lanes, might guess is you wouldn't see it much,” Magalotti said.
With increased population during the height of the region’s manufacturing economy, roads became more congested. Adding a lane wasn’t always possible and it can be expensive to put a green turn arrow.
“People who commute on a daily basis, one way or another will find a way as long as that decision that they are considering are bringing more benefits than costs,” said Stevanovic.
Newcomers and new drivers
When major manufacturers left Pittsburgh, much of the city’s population went with it. According to census data, between 1950 and 2010, 370,955 people moved out of the city. When higher education, health care and technology reemerged as the new economic drivers, the people moving in often weren’t from here and therefore unfamiliar with the practice.
This was the experience of Good Question! asker Bob Paczula.
“As an immigrant to Pittsburgh from central Ohio where it’s flat and road are perpendicular to each other, it took some time to adapt to Pittsburgh driving,” Paczula said. “I am aware of it now. I'm still not a fan.”
For people new to driving, Cindy Cohen of the Cindy Cohen School of Driving, said she makes students aware, but emphasizes that it is technically illegal.
“I teach the students to stay behind the white line,” Cohen said. “And to wait until it’s their turn. Sometimes it just takes a long time, but that’s what the law says.”
Pennsylvania law dictates left-turning drivers must yield to oncoming traffic. As new drivers study the state’s driving law, Tim Rogers with Rogers Driving School said students do ask about the practice and how best to approach a situation at an intersection.
“I always explain the situation of courtesy that people are letting you go,” Rogers said. “But yes, be careful if you’re going to do that because you never know what might be happening if you make a left. There could be a car coming and you can encounter that car and have an accident.”
Plus, there are bicyclists and pedestrians to consider. Taking a Pittsburgh left improperly could mean putting these travelers in danger.
The by-the-book approach is typically how the city’s recent fleet of self-driving vehicles are trained when they hit the roads, according to Carnegie Mellon University research professor Jeff Schneider. He was part of the team to found Uber’s autonomous vehicle division in 2015.
“We would never program our own cars to do something that, you know, wasn’t legally the right thing to do,” Schneider said. “The part that is not avoidable is dealing with the fact that other drivers on the road will be doing the Pittsburgh left.”
These vehicles are constantly collecting data about other drivers’ behaviors, which is where Schneider says machine learning comes into play.
“Essentially when we collect all the data from other cars driving around the streets, eventually the learning algorithms will see that pattern,” Schneider said.
These patterns will help the self-driving cars recognize behaviors like the left. But Brett Browning, executive vice president of product development and chief technology officer at Argo AI, said don’t expect the self-driving cars to ever take the left. Rather, they’ll be aware that someone might pull out in front of them.
“We want the cars to be very predictable,” Browning said. “And so that means you have to drive like the local social norms.”
The city isn’t as populated and congested as it used to be, so need for the Pittsburgh left has diminished. Even so, it’s part of the region’s cultural heritage.