A driverless shuttle school bus service in the US has been halted with authorities saying its testing was putting students at an "inappropriate" risk.
The National Highway Traffic Safety Administration on Monday said it had ordered Transdev North America to immediately stop the shuttle in Florida.
The auto safety agency known as NHTSA said in an order issued late on Friday that Transdev's use of its EZ10 Generation II driverless shuttle in the Babcock Ranch community in southwest Florida was "unlawful and in violation of the company's temporary importation authorisation."
"Innovation must not come at the risk of public safety," said Deputy NHTSA Administrator Heidi King in a statement.
"Using a non-compliant test vehicle to transport children is irresponsible, inappropriate, and in direct violation of the terms of Transdev's approved test project."
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In March, NHTSA granted Transdev permission to temporarily import the driverless shuttle for testing and demonstration purposes, but not as a school bus.
The agency said the company had agreed to halt the tests. A spokeswoman for Transdev did not respond to several requests for comment on Monday.
Transdev North America is a unit of Transdev, which is controlled by France state-owned investment fund Caisse des Depots et Consignations.
The company in August issued a news release saying it would "operate school shuttle service starting this fall with an autonomous vehicle, the first in the world."
Transdev said the 12-person shuttle bus would operate from a designated pick-up area with a safety attendant on board, would travel at a top speed of 13km/h with the potential to reach speeds of 48km/h once additional infrastructure was completed.
