Whether autonomous vehicles (AVs) will decrease or increase traffic is a surprisingly complicated question. AVs will not only affect how people commute, but could also change how populations are distributed and how cities are designed. Although there are plenty of uncertain factors at this point, the following outlines ways AVs could impact the future of traffic congestion.

First, how AVs operate will be different than a vehicle with a human driver. AVs will drive more slowly and carefully, especially in downtown areas. Because of this, AVs could lead to increased congestion as they look for drop-off and pick up spots, wait for another car to parallel park, or while finding another person waiting for a ride as they shift into taxi-cab mode. On the other hand, AVs will drive at a more constant rate of speed. Reducing the amount of slowing down, then speeding up will decrease congestion and improve the flow of traffic. Because of the chain reaction caused by a human driver hitting their brakes, a National Science Foundation study found that a single self-driving car can influence the traffic flow of at least 20 human-controlled automobiles around it. 

AVs will also create space, both on and off the road. On the road, AVs can travel closer together than human operated cars, creating space for more cars within existing lanes opening up the road  for alternative forms of transportation, such as trams/streetcars, Bus Rapid Transit systems, bikes, and scooters. Off the road, the need for parking lots will greatly diminish. AVs can drive themselves to a convenient area to park instead of a human driver wanting to park close to their destination. It has been estimated that around 30% of land in U.S. cities is taken up by parking. In a full switch to AVs, it is estimated that 90% of this space can be repurposed. In major cities, this extra space could create more housing, putting more people within range of alternative forms of transportation, such as the subway. 

However, the convenience of AVs will also cause people to find their time commuting less burdensome, increasing their willingness to drive. Without having to focus on the road, a passenger could work, relax, or even take a nap. AVs increasing people’s willingness to drive could also expand the problem of urban sprawl. The convenience of AVs could also shift demand from alternative methods of transportation that reduce traffic congestion, such as busses, trains, and even airplanes. Because AVs don’t require a driver, children, the elderly, and people with medical conditions that preventing them from operating a vehicle will also be able to ride in a car by themselves, increasing traffic further. 

Instead of promoting urban sprawl, an alternative theory is that AVs might enable city planners to create ‘semi-urban nodes.’  These spaces would take advantage to the space freed up by parking lots that are no longer necessary to create new communities away from urban areas. More and more of the population could shift to living around ‘semi-urban nodes’ and rely upon walking or biking to travel around them. However, most towns’ current zoning laws prohibit the mixing of commercial and residential property, which is necessary to create these nodes.    

Some key variables that will shape the future of AVs and congestion are people’s willingness to share AVs and how much space AVs free up. If people can’t afford to buy an AV, they will be forced to share AVs with others. How quickly AVs will become affordable to the masses for purchase is unclear. However, the new Tesla Model 3, with limited self-driving capabilities, currently starts at $35,000 MSRP. That price is significantly cheaper than the first Model S to offer this feature. Even if people are willing to share AVs, how much will they be willing to share rides with others?  If the public reception to UberPOOL and Lyft Line is any indication, sharing rides will not be popular. A possible solution is to discourage solo driving by imposing a tax on those who drive alone. Alternatively, giving shared driverless rides their own dedicated, high-speed lanes could incentivize more sharing of AVs.