There's been a lot of work done in this area, with predictable backlash. I think the issue is that the most dangerous speeding is the kind which occurs in neighbourhoods and by schools ("50km/h in a 30km/h zone"). But the easiest to apply automatic enforcement against is highway speeding ("130km/h in a 100km/h zone"), so people legitimately complain that the enforcement isn't being applied where the danger is.

The worst of it is that all the infrastructure is in place already for average speed enforcement on toll roads, since you know when everyone gets on and off the highway and all their license plates. But isn't the whole point of a toll road that you pay for the privilege of being out of traffic and going as fast as you can? Who wants to pay for a toll transponder only to get a bunch of speeding tickets in the mail the next month?