Self-driving cars could be terrible for traffic — here's why

Execs like Google cofounder Sergey Brin have touted traffic reduction as one of the many benefits of having self-driving cars on the road. The idea is that autonomous cars will eliminate accidents caused by human error, a major contributor to traffic.

But experts say the vehicles' impact on traffic will either be minimal or negative.

Lew Fulton, a co-director at UC Davis' Institute of Transportation Studies (ITP), told Business Insider that autonomous vehicles won't fix congestion woes unless a pricing system is put in place that discourages zero-occupancy vehicles.

"We are especially concerned about zero-occupant vehicles that can happen with automated vehicles," Fulton said. "That scenario is especially plausible with private ownership of those vehicles and no limits to what we can do with them."

For example, many companies are interested in programming autonomous cars to run errands or pick-up packages, but these efforts could increase traffic by multiplying the number of zero-occupant cars, or "zombie cars," on the road, Fulton said.

Massachusetts lawmakers have already proposed a tax on driverless vehicles to prevent zombie cars. The bill calls for a per-mile fee of at least $0.025.

Congestion could also worsen as companies like Lucid Motors explore designing self-driving vehicles around comfort, like installing reclining seats.

Consumers may opt to live farther outside of cities if they can commute in vehicles that allow them to sleep and relax. But that sprawl increases the number of people traveling in and out of cities during rush hour, Fulton said.

Self-driving cars can still contribute to congestion even if they operate as part of a ride-hailing network, like Uber.

Without the cost of a driver, Fulton said he worries self-driving Ubers or Lyfts will become so cheap there will be no financial incentive to opt for car-sharing services like UberPOOL.

"I think it's going to take some kind of pricing system that discourages zero-occupant vehicles and also makes penalties for single-occupancy vehicles," he said.

Fulton isn't alone in this line of thinking.

Matthew Turner, an economist at Brown University, has studied road congestion and co-authored a 2011 paper titled "The Fundamental Law of Road Congestion." Turner found that vehicle pricing structures have had the biggest effect on reducing travel time, more so than increasing public transit access.

"Maybe autonomous cars will be different from other capacity expansions, but of the things we have observed so far, the only thing that really drives down travel times is pricing," Turner told the New York Times.

Some cities have already mobilized to discourage people from taking cars alone. States like California and Colorado have installed high-occupancy toll lanes that single-occupancy must pay a fee to use. That fee increases during rush hour.

"We have to figure out systems that promote pairing," Fulton said. "It really is a silver bullet if we can do it."

Self-driving cars could be terrible for traffic — here's why

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