When the urban autonomous vehicle (AV) traffic jams start, don’t blame the cars. They’re just doing what they’re told. Blame people. We’re the problem.

University of California Santa Cruz Environmental Studies Professor Adam Millard-Ball predicts an obvious, depressing problem that could derail the vision of AVs efficiently moving people around city centers while reducing the number of vehicles on the road – parking.

High parking costs are a tactic that cities use to discourage people from bringing cars downtown, and AVs could eliminate that disincentive. People could ride their self-driving cars to the baseball stadium, then put the AVs in lurk mode – telling them to slowly circle the area for a few hours. Fuel costsl would be significantly lower than the $40 peak pricing associated with game days. Sound ridiculous? Look at airport baggage claim areas lately where people crawl at 0.5mph to comply with no parking rules.

“Parking accounts for a large share of the marginal costs of vehicle use in urban areas, so AVs would dramatically reduce the cost of car travel and increase demand – more than double in downtowns such as San Francisco,” Millard-Ball says. Eliminating parking costs makes bringing cars into congested areas more attractive, so more people would do so, increasing congestion.

His paper, “The Autonomous Vehicle Parking Problem” in Transport Policy predicts that as few as 2,000 AVs in downtown San Francisco would lower the average commute speed to 2mph.

Proponents of AVs often discuss a future where cars are autonomous and shared – robo-taxis that pick people up and drop them off, staying in constant use. In that vision, parking isn’t a problem because a person would take one car to the baseball stadium, the vehicle would then pick someone up in that area and take them back out of the city center. At the end of the game, another autonomous car would pick up the sports fan, taking him home.

Millard-Ball says the problem with that vision is traffic patterns are clumpy – people tend to go to the same places at the same time and leave at the same time. People arrive at baseball games before the first pitch and leave after nine innings.

“Sharing of AVs could, in many respects, make the problems worse,” Millard-Ball says. “First, it would reduce the cost of parking even further below the estimates in the paper… Second, transportation demand is highly peaked. In the middle of the day, many shared AVs would be idle and would need to park or cruise.”

Millard-Ball says the only regulatory framework that could discourage AVs from further congesting downtowns would be fees for bringing cars into the city center, something already occurring in London, England. He doesn’t believe technological efforts, such as a ban on creep modes, could work because it’s hard to legislate intent.

For technology companies pushing AV systems and the automakers that want to adopt them, the parking/congestion issue is something that must be addressed before these vehicles become common. Companies smart enough to design vehicles that manage themselves should be bright enough to teach those AVs not to be jerks.