Jones called Williams for help and he arrived at the scene of the accident in a city-owned Ford Explorer, police said. Police noticed that he was visibly intoxicated and he also was arrested for DUI, police spokeswoman Tanya Little said.
A sergeant-at-arms was described as a low-level patronage job whose function is to assist council members.
The two vehicles were towed to a police lot as part of the investigation, Little said.
The Cobalt and Explorer are part of the city fleet to be checked out to transport council members or their aides to meetings around Philadelphia, city officials said.
Jane Roh, communications director for Clarke, said that it was a "flat-out unauthorized use of the cars" and in a subsequent e-mail said the incidents could be "immediate grounds for firings."
Clarke, in a statement, said the incidents, "if confirmed by the authorities, display a level of conduct and disregard for public safety that cannot be tolerated."
Clarke said he would wait until the police investigation is completed before taking "appropriate action."
While a sergeant-at-arms could be authorized to use a city-owned vehicle, a receptionist would have no reason to use one, Roh said. "You can't just grab a key and take a city vehicle," she said.
Mayor Nutter spokesman Mark McDonald referred questions to Clarke's office.
Contact staff writer Bob Fernandez at firstname.lastname@example.org or 215-854-2771