San Francisco, Aug 19 (IANS): The US regulators have told Cruise, the self-driving car subsidiary of General Motors, to immediately reduce its robotaxi fleet by 50 per cent following a crash of its car with a fire truck.

The California Department of Motor Vehicles (DMV) said it is investigating "recent concerning incidents" involving Cruise vehicles in San Francisco.

The regulatory agency told Cruise to have no more than 50 driverless vehicles in operation during the day and 150 driverless vehicles in operation at night, till the investigation is complete, reports TechCrunch.

"Safety of the traveling public is the California DMV's top priority. The primary focus of the DMV’s regulations is the safe operation of autonomous vehicles and safety of the public who share the road with these vehicles," the department said in a statement.

In a blog post, Cruise said that while the investigation is going on, "we wanted to provide an update on our preliminary analysis on the incident involving an emergency vehicle colliding with a Cruise AV."

"The Cruise AV did identify the risk of a collision and initiated a braking maneuver, reducing its speed, but was ultimately unable to avoid the collision," said the company. During the course of more than 3 million miles of fully autonomous driving in San Francisco, "we've seen an enormous number of emergency vehicles - more than 168,000 interactions just in the first seven months of this year alone”, it added.

The automaker said that Cruise AVs have the ability to detect emergency sirens, which increase their ability to operate safely around emergency vehicles and accompanying scenes.

"In this instance, the AV identified the siren as soon as it was distinguishable from the background noise," said Cruise.

Last week, regulators in California gave the green signal to autonomous car companies Cruise and Waymo to run commercial robotaxi services across San Francisco 24/7.