A small fleet of Cruise robotaxis in San Francisco suddenly stopped operating on Tuesday night, effectively stopping traffic on a street in the city's Fillmore district for a couple of hours until employees were able to arrive. TechCrunch first noticed a Reddit post that featured a photo of the stalled driverless cabs at the corner of Gough and Fulton streets. Cruise -- which is General Motor's AV subsidiary -- only launched its commercial robotaxi service in the city last week. The rides feature no human safety driver, are geo-restricted to certain streets and can only operate in the late evening hours. Cruise apologized for the incident in a statement, but gave little explanation for what caused the mishap.