The Fast Lane was the lowest level of the Motorway in New New York around the year 5000000053. The motorway was a route for flying cars to travel long distances. In the majority of the levels of the Motorway, it would take years, occasionally even decades, for one to reach its destination a few miles away. However, if a car carried three or more passengers, they could request access to the fast lane at the very bottom of the motorway. Because few cars were in the fast lane, the journey was thought to take less time than in the other lanes because of the ability to "get up to thirty mph".
However, there were many stories about cars which had gone missing after going to the fast lane. This was because the Macra lived at the bottom of the motorway, living off of the fumes coming from the cars above. (TV: Gridlock)