Getting Up to Speed

Driverless cars might be the key to solving traffic woes

If you haven’t taken a ride in a driverless car yet, odds are you will soon. Waymo operates in the San Francisco Bay Area, Los Angeles, Phoenix, Austin, and Atlanta. It has expansion plans for New York City, Denver, Seattle, Miami, Washington, D.C., and Dallas. Uber is investing $300 million in Lucid’s robotaxi program with plans for 20,000 driverless cars on the road in the next six years. Amazon’s Zoox is giving rides in Las Vegas and is on its way to San Francisco. The number of automated vehicles on the road is set to skyrocket in the next few years. What effect, we wonder, will that have on traffic patterns?

Stops & Starts

Human drivers have a tendency to create “phantom congestion,” where one person steps on the brakes, then a line of trailing cars also slows down. This pattern repeats, often because someone is following the car ahead too closely.

Automated cars, on the other hand, keep an even distance between themselves and the car in front of them.

“Driving is very intuitive. If there’s a gap in front of you, you accelerate. If someone brakes, you slow down. But it turns out that this very normal reaction can lead to stop-and-go traffic and energy inefficiency,” said Alexandre Bayen, associate provost and engineering professor at the University of California, Berkeley. “That’s precisely what AI technology is able to fix — it can direct the vehicle to things that are not intuitive to humans, but are overall more efficient.”

Bayen led a CIRCLES Consortium experiment that deployed a fleet of 100 Nissan Rogue, Toyota RAV4, and Cadillac XT5 vehicles on Nashville’s I-24 during rush hour for five days. The trial showed that by driving at a consistent speed, rather than starting and stopping, just a few automated vehicles could even out the flow of traffic, saving energy and preventing unnecessary traffic jams.

Sharing the Road

As driverless cars become the norm, we can expect car ownership to go down, with ride-sharing robotaxis in near-continuous operation.

“I don’t know what the future will look like, but I hope it will be shared and electric because then you can reduce the number of cars because most of the time” cars are parked, Oren Ezer, co-founder and CEO of Electreon, which makes wireless EV charging infrastructure, told Reboot.

Scholarly predictions and NHTSA studies indicate that even with fewer cars on the road, there would be a “rebound” effect in which the popularity of robotaxis leads to more total hours on the road per vehicle. Riders, for instance, would rely less on public transportation in favor of on-demand transportation. People who can’t or don’t drive would take advantage of the convenience robotaxis offer to take more car trips. The NHTSA concluded that the rebound rate would stabilize at around 10%, meaning that even with induced demand, traffic dominated by driverless cars would lead to fewer cars on the road and reduce delays.

Based on the rates of adoption for previous technological innovations in vehicles – things like automatic transmission and air bags – the Victoria Transport Policy Institute projects that in the 2050s, 40-60% of new vehicle sales will be automated, with driverless cars accounting for 30-50% of automobile travel. A decade later, VTPI says, nearly all new sales will be automated vehicles, accounting for 50-80% of car travel.

Making Connections

For automated vehicles to really improve traffic, though, they need to be able to talk to each other. Otherwise, they can actually slow things down.

“We found that higher percentages of AVs – which are not connected – actually slows travel times through intersections,” Ali Hajbabaie, an associate professor of civil, construction, and environmental engineering at North Carolina State University, said. “This is because those AVs are programmed to drive conservatively in order to reduce the risk of collisions. Our findings underscore the importance of incorporating connectivity into both vehicles and traffic-control systems.”

Running traffic simulations, Hajbabaie and his team found that the more connected vehicles there are on the road, the more can flow through intersections quickly and avoid being stuck at red lights.

“There is a lot of research showing that automated vehicles can improve safety. But our research here – which relies on computational modeling – suggests that if we want to also improve travel time, an increase in automated vehicles isn’t enough; we need vehicles that are capable of communicating with each other and with the traffic-control systems that manage traffic flow at intersections.”

Communicating to avoid colliding with one another, driverless cars can feel free to move through an intersection without excessive caution that can cause traffic jams.

Safer Streets

That tendency of automated vehicles to be cautious is overall a good thing. NHTSA figures show that traffic accidents kill roughly 40,000 people in the U.S. annually, and that 90% of them are caused by human error.

To be sure, driverless cars have also caused fatal accidents, and for reasons like software or hardware glitches that would not happen to a human driver. But on balance, analysis and projections show, automated cars will bring the number of fatalities down. Saving lives is obviously its own reward, but a significant reduction in crashes would also alleviate traffic jams, as at least a quarter of them are attributable to accidents.

A shift to a majority of cars on the road being driverless will necessitate some redesign to make markings and signs clearly visible to their cameras as well as to human eyes. In the long term, the shift could lead to a complete rethinking of how we use roads. Implementing dynamic traffic lights that adjust to traffic flow in real time could cut down even further on congestion. Having fewer cars on the road to accommodate could lead city planners to install more bike lanes and pedestrian-only zones. Automated systems could be designed to prevent delivery vehicles from stopping in roadways and causing backups.

“Our vision is that eventually, this technology will be deployed in many, if not all, vehicles, and we are working on ways to make it scalable to the public,” CIRCLE’s Consortium’s Jonathan Lee said.

If so, sitting in traffic might be a thing of the past.