As critical as I am of the federal government, I do have to say something in their defense here. I once worked for the US Attorneys Office in Chicago, so I am familiar with a number of federal employees who drive government cars.
Will only speak of those I know about. FBI and Customs agents that I knew probably had a government car to drive--not all however. DEA usually drove vehicles confiscated from drug dealers. Postal Inspectors got a car when necessary.
As for the Labor Dept., I have a friend who is a manager for the CPI. She is allowed a car if she is going out of town on government business--the rest of the time she takes the commuter train back and forth to the federal building like any other peon.