dave, I'm guessing the 'benefits of the road' (which I've never been on) are that it's empty. Fill it up with people driving at a discount and the benefits are reduced.
If you drive down Florida, you can use the old Highway One, crawling through towns, or the interstate, or a turnpike (toll road). The turnpike is great if you just want to get somewhere in the least possible time, with no billboards and not a lot of traffic. I suspect it's the 'business class road', used by travelling salespersons and the like who can claim it on expenses (though it's not hugely expensive). But most people use the free insterstate.
However, I doubt Britain has the space to have three roads running along the same route.