SPECS the next instalment

I see the SPECS cameras are now live on the A14
One thing that our wonderfull leaders have not rumbled is that average speed is a complicated thing. You can travel a distance at one speed, say 60mph. If you then have to slow for a couple of miles to say 50 (like behind a lorry that has pulled out in front of you with no indication) Once he pulls in, you can then drive several miles at 65 mph and still not exceed the overall average for any given distance. I can supply the formulae if anyone is interested.
But as that requires a little working out, I doubt if our leaders would know how to do it.