The Rev Dodgson said:

ChrispenEvan said:

A vehicle passing at any speed will trigger the camera, so you will have to have an average speed of exactly 0 km/h not to trigger it*.

If they mean how fast can you go and not get a fine, an average speed of 120 km/h over the second half will give you a travel time of 15 minutes overall, which is 80 km/h, so assuming this is in a civilised state with some tolerance on speed limits, you can go well over that. 125 km/hr should be safe.

• Actually there must be some finite speed required to trigger the camera, so you could go as fast as you like, then slow down to less than trigger speed as you pass the camera.
  

average speed camera work purely on time, not speed. they take a pic at the start then another at the finish. match number plates and calculate.