Here is the sign progression:
Mile 1: When traffic flows freely, the variable speed limit signs are black
Mile 1.5 Seconds after a collision occurs three miles up the highway, the speed limit drops and a sign warns drivers of backups ahead
Mile 2: As vehicles approach the collision area, the speed drops again.
Mile 2.5: A mile from the trouble spot speed limit signs flash arrows intermittently. Green arrows instruct drivers to proceed in their lane, and yellow arrows mean exit the lane as soon as safely possible, because the lane is closed or blocked ahead.
Mile 3: At the site of the collision, red X’s indicate which lanes are blocked.