Two companies race to deploy robotaxis in San Francisco. The city wants them to hit the brakes.

The city’s transportation officials sent letters this week to California regulators asking them to halt or scale back the expansion plans of Cruise and Waymo.

A Cruise autonomous vehicle is displayed in Detroit on Jan. 16, 2019.Paul Sancya / AP file

SAN FRANCISCO — San Francisco is trying to slow the expansion of robotaxis after repeated incidents in which cars without drivers stopped and idled in the middle of the street for no obvious reason, delaying bus riders and disrupting the work of firefighters. 

The city’s transportation officials sent letters this week to California regulators asking them to halt or scale back the expansion plans of two companies, Cruise and Waymo, which are competing head-to-head to be the first to offer 24-hour robotaxi service in the country’s best-known tech hub. 

The outcome will determine how quickly San Francisco and possibly other cities forge ahead with driverless technology that could remake the world’s cities and potentially save some of the 40,000 people killed each year in American traffic crashes.

The episode adds another chapter to the complicated history of self-driving cars, an idea that has been teased by technologists as a possibility in the future while facing a variety of setbacks in the past few years. Waymo offers fully autonomous rides in Phoenix, while Tesla lets some of its owners test “driver assistance” features that are the subject of a federal investigation. A self-driving Uber test vehicle struck and killed a woman in 2018. 

Some believe self-driving cars will never happen on a wide scale, but they’ve been gaining momentum in San Francisco. 

Cruise, which is majority-owned by General Motors, won permission last year to use 30 vehicles as robotaxis in parts of San Francisco between 10 p.m. and 6 a.m. The vehicles do not have backup human drivers during that time. The company has since received permission to test driverless cars any time of day, but it needs a signoff from the California Public Utilities Commission to expand the hours of its commercial service. 

Neither vehicles from Cruise or Waymo have killed anyone on the streets of San Francisco, but the companies need to overcome their sometimes comical errors, including one episode last year in which a Cruise car with nobody in it slowly tried to flee from a police officer

In one recent instance documented on social media and noted by city officials, five disabled Cruise vehicles in San Francisco’s Mission District blocked a street so completely that a city bus with 45 riders couldn’t get through and was delayed for at least 13 minutes. Cruise’s autonomous cars have also interfered with active firefighting, and firefighters once shattered a car’s window to prevent it from driving over their firehoses, the city said. 

San Francisco officials said they want to continue the experiment and to even allow Cruise and Waymo to expand, but only if they do so slowly and with conditions. 

“A series of limited deployments with incremental expansions — rather than unlimited authorizations — offer the best path toward public confidence in driving automation and industry success in San Francisco and beyond,” three city officials wrote Thursday in a letter to the utilities commission, the state agency that decides if a company gets a robotaxi license. A second letter expressed concerns about Waymo. 

San Francisco doesn’t want robotaxis operating in the city’s downtown core, for example, or during morning and evening peak commuting times. And it wants more data on how the vehicles perform. 

Last month, the National Highway Traffic Safety Administration said it was investigating the same issues including blocked traffic. 

Cruise has argued that its service is safer than the status quo. 

“Cruise’s safety record is publicly reported and includes having driven millions of miles in an extremely complex urban environment with zero life-threatening injuries or fatalities,” Cruise spokesperson Drew Pusateri said in a statement Friday. 

He also provided letters in support of Cruise written by local San Francisco merchants associations, disability advocates and community groups. 

San Francisco is failing to make progress on its “vision zero” goal of no traffic deaths by 2024. Last year, there were 37 traffic fatalities in the city, an increase from 31 fatalities in 2014 when it adopted the goal. 

City officials argue that stopped robotaxis are hazards that can cause human drivers to react dangerously. 

“They can cause other vehicles to make dangerous abrupt lane changes, brake or accelerate rapidly, or veer into bike lanes or crosswalks. They can cause rear end collisions,” they wrote in their letter to the state regulator. 

U.S. Transportation Secretary Pete Buttigieg has called the national rise in auto deaths a crisis and all but endorsed a move to autonomous vehicles. 

“Frankly, it would be hard to do worse than human drivers when it comes to what we could get to theoretically with the right kind of safe autonomous driving,” he told Quartz last year. 

Waymo, which shares a parent company with Google, has tested its technology in San Francisco but has not given rides to paying members of the public in the city without a safety driver. As a result, Waymo hasn’t had the same high-profile unplanned stops as Cruise — though it has had diffficulty with one dead-end street — but the city still wants the company to take it slow on the way to a 24-hour robotaxi service. 

Waymo said Friday it wants to keep talking with the city. 

“These letters are a standard part of the regulatory process, and we have long appreciated a healthy dialogue with city officials and government agencies in California,” the company said in a statement, adding that it would elaborate in a written submission to regulators next week.