There isn’t a policeman hiding behind the pit wall with a radar gun and there aren’t speedometers in NASCAR racing vehicles. So how do teams and officials measure pit-road speed limits with a certain amount of precision?

For NASCAR officials, the answer lies in scoring loops, a series of electronic sensors below the pit road pavement which calculate time over distance to measure car speed. The speed limit varies from track to track, depending on the facility’s size – it can be as slow as 30 mph at short tracks such as Bristol and Martinsville, and as fast as 55 mph at superspeedways such as Pocono and Talladega.

For drivers, the trick to staying within the limits is based on their tachometer readings. Teams can program their tachs before the race to know which amount of RPM (revolutions per minute) equals the legal pit road speed.

NASCAR rules allow for a 5-mph buffer over the posted speed limit; it’s a cushion that teams exploit on a regular basis.