If you are approaching any type of authorized emergency vehicle parked on a two-lane roadway with their lights flashing, you must slow to a speed that is less than the posted speed limit, when it is over 25 mph.

The answer is 20 miles per hour. If you are approaching any type of authorized emergency vehicle parked on a two-lane roadway with their lights flashing, you must slow to a speed is 20 mph less than the posted speed limit. The reason is so that the normal flow of traffic does hinder the emergency responders from doing their jobs which often times means the saving of lives. This law reduces the speed of the normal flow of traffic for this purpose.