If there is one its a traffic counter, if there are a pair they are for speed or both. The guy who ran the speed awarness course I was on showed me a graph of results from one outside a school during term time between 3 and 4 pm, cars going as fast as 60mph right outside a school.
Helps them decide where to put cameras and speedhumps.
	
		
			
		
		
	
				
			Helps them decide where to put cameras and speedhumps.