Due to safety concerns, San Francisco transportation officials want Waymo and Cruise to halt the growth of their robotaxi services in the city.

This comes after numerous instances in which unoccupied cars stopped and idling in the middle of the street for no apparent reason, delaying bus users and impeding firefighters' work.

Spontaneous Halts Result In Traffic Disruptions

The expansion of either service, according to the San Francisco County Transportation Authority officials, is "unreasonable," The Verge writes. 

This given previous instances of autonomous cars blocking traffic and hindering emergency personnel, as indicated in a letter to the California Public Utilities Commission.

Currently, the only companies authorized to provide customers with driverless rides in San Francisco are Alphabet-owned Waymo and Cruise, which are funded by GM.

In June, Cruise was granted permission to charge passengers for use of its automated vehicles (AV) between the hours of 10 p.m. and 6 a.m..

A few months later, Waymo was granted permission to provide totally driverless rides, but the company still can not charge drivers for driverless trips.

It can be remembered that when a fleet of driverless Cruise cars mysteriously stopped working in July and again in September, they halted traffic for hours.

Earlier this month, a driverless Waymo vehicle that halted in the middle of an intersection in San Francisco caused a traffic gridlock.

Read More: Waymo Will Bring Robotaxi Operations to Los Angeles 

Faulty Robotaxis Are Now Being Investigated

Due to worries that the vehicles were obstructing traffic and causing rear-end incidents with abrupt braking, the National Highway Traffic Safety Administration started an investigation into Cruise last December.

However, the way driverless vehicles interact with emergency vehicles worries city officials as well, according to The Verge.

In April of last year, according to officials, an autonomous Cruise vehicle "created an obstruction for a San Francisco Fire Department vehicle on its way to a 3 alarm fire" by stopping in a travel lane.

It can be remembered that a Cruise AV later ran over a fire hose that was being used at an active fire site.

Earlier this month, another Cruise vehicle came dangerously close to doing the same at an active firefighting incident.

Other examples involve Cruise dialing 911 three times for "unresponsive" passengers, only for the emergency services to show up and discover that the person had simply fallen asleep.

The San Francisco Transportation Authority supports the development of driverless technology but calls for increased openness and safety measures.

According to officials, companies should be forced to gather more information about the performance of the vehicles, such as how frequently and for how long their driverless cars obstruct traffic.

Until they can regularly operate "without significant interruption of street operations and transit services," it also wants to prevent AV businesses from operating on San Francisco's "downtown core streets" during peak travel times.

Despite receiving clearance from the California Department of Motor Vehicles in December, the company is still awaiting CPUC's approval.

Both companies provide transportation services in Phoenix, Arizona, and Cruise also expanded its robotaxi service to Austin, Texas.

Related Article: GM's Cruise Launches Robotaxi Services in Austin, Phoenix