How NASCAR Freezes the Field
Timing & Scores Loops (A - H)
Freezing The Field
In an effort to further ensure the competitors' safety, NASCAR announced in September of 2003 that racing back to the caution would no longer be permitted in the NASCAR Sprint Cup Series, NASCAR nationwide Series and NASCAR Craftsman Truck Series. That led NASCAR to institute a new procedure in which the field is "frozen" on the race track once the caution flag is issued.
The cars' positions are determined by the previous timing-and-scoring line they passed on the race track. Example: Cars Nos. 1 through 3 are scored by their running order when the passed timing and scoring line E; cars Nos. 4 and 5 are scored by their positions when they passed timing and scoring line D; cars 6 and 7 are scored by their positions when they they passed timing and scoring line
While the positions of the competitors on the race track will be "frozen," the pit lane, however, will remain active at this time with pit-road speed in effect.
The cars that are pitted from pit-road entrance to the start/finish line - cars 11, 12, 14 and 14 - must reach the start/finish scoring line that extends across pit road before the race leader (No. 1 red car approaching scoring line A) reaches the same line on the race track. Should any of these cars on pit road reach that point first, they will not lose a lap to the leader.
Should the leader reach the scoring line A before cars 11 - 14, they would lose a lap to the leader. Those cars that are pitted from the start/finish line to the pit-road exit - cars 8, 9 and 10 - must reach the pit-road exit scoring line before the leader (No, 1 red car approaching scoring line B) to avoid going a lap down.
Example: car 8 would not go a lap down, while cars 9 and 10 would. Should a driver attempt to speed in pit lane to avoid going down a lap to the leader, that driver will lose a lap in addition to being moved to the tail end of the longest line.
Should the race leader not slow immediately for the caution in an effort to put the pitted cars a lap down, the leader will be penalized by being sent to the tail end of the longest line and all pitted cars will retain their lap positions.
Adapted from information by NASCAR Media