The W Road was closed Tuesday evening after a slick spill about a half-mile in length, according to a 911 Center supervisor.
Another 911 supervisor said the W Road would be closed until this morning, but she wasn't sure what time it might reopen.
The spill started at the "second W curve" from the top, coming down half a mile between Anderson Pike and Seagle Drive, she said.
About 10 p.m. Tuesday, officials did not yet know what the spilled substance was, she said, but it was "some sort of oil or gasoline as far as they could tell."
Callers told county dispatchers that cars could not negotiate the steep roadway because of the substance.
A hazardous materials specialist was dispatched to Anderson Pike between the W Road and Gardenhire Avenue at about 7:30 p.m., she said.
Highway officials spread sand over the road, the dispatcher said.