[ThrustVectoring]

Enforcing a speed limit on freeways is completely possible. They've got it done in England. What you need to do is capture license plates on entrance and exit, and calculate the average speed for each car's trip. If the speed limit is 50 MPH for traffic-flow reasons, and you do your 15 mile commute in 15 minutes, you're getting a "60 in a 50 MPH zone" ticket in the mail, every single time.

People will learn in a hurry that speeding is pretty much pointless and self-harming.

[noarchy]

They've really got the surveillance state thing down to a science there, if they're doing things like that. In North America, where there are cameras, they tend to only look at your speed at a specific moment.

[bsder]

This works in the UK because

1) a lot of non-artery roads are really shitty in the UK 2) the UK is an island with lots of rivers and lakes so you may not have an option besides that particular road 3) UK average trips are likely much shorter

If they enforced speed limits on roads in the US with that technique, that road would simply stop being used. There are almost always other options, and the further you are traveling, the more options there are.