As for the speed, it’s nowhere near ‘i want to die’ reckless for those long sweepers and a lot of people do find the rhythm of that sort of driving to be relaxing. The other component is simply that the sensation of speed is always much lower than it would be in real life in these kind of things.
It's a bit like a "ambient study music" site that plays darkstep with flashing lights when you press "just play me something to study to" =)
maybe you can add a self learning component. every time the vehicle bumps the barrier, it was going/accelerating to fast.
Basic physics is also pretty applicable here. ;)
acceleration = velocity^2 /radius
with a simplified
max friction force = coefficient of friction * car weight
And to tie them together
force = mass * acceleration
No going 115+ in a blind corner over a road that will launch you off the side of a mountain if you steer poorly =D
This also makes for an excellent emergency budget fill-ups at the end of the quarter - just set a photoradar in the 50 zone where everyone everyday go 80 and, voila, - no deficit.
I assume that's because there are some roads still left where they're trusting drivers' common sense to not try to drive as fast as they're theoretically allowed to.
Anyway, good job, actually cool!