in the US, there is no state that allows you to exceed 65mph that I'm aware of, and yet domestic cars are sold with the ability to go 120mph plus. Sure, you can jam your foot on the pedal and go as fast as you want.. but you're breaking the law. I wonder how many unnecessary injuries and deaths could be prevented if cars simply could not exceed the maximum speed limit
There are some portions of freeways in California (i believe highways 5 and 40) with posted speed limits of 70-75. But that's a minor point. Evasive action is sometimes necessary by a (hopefully responsible) driver, and being able to crank a vehicle up faster than the speed limit for brief durations offers additional maneuverability. I do this once in a while. I realize you're mostly referring to people that drive higher than these speeds continuously.
Also, what to do on a three-lane highway when all three lanes are going 65 mph, and there are three cars running parallel across the three lanes, and an ambulance pulls up behind the vehicle on the left? The automobile driver would actually have to slow down to let the ambulance pass. As the ambulance continued along the highway and encountered additional parallel cars like this, choosing to stay in the left "passing" lane would actually force the ambulance to slow down below 65 so that the vehicle in the left lane (the one responsible for providing right-of-way) can slow down and get behind the car to his right with which he was previously parallel. You often can't count on the drivers in the other lanes to slow down and let the ambulance-blocking driver pass in front.
Let's say all personal vehicles were manufactured with a top speed of 80 mph. How would the speed of the vehicle be limited? A car and its engine with a maximum speed of 120 mph might offer a smooth, comfortable, and fuel-efficient ride around 70 mph, but when accelerated beyond that, the car will start to vibrate, and the efficiency of the engine will decline. I fear that designing cars with top speeds of some arbitrary speed limit, plus a few extra mph for cushion, could hinder the driving experience. In another scenario, fuel consumption could be limited on existing vehicle designs to support a maximum speed and nothing more. But would that work correctly on hills, in snow, or in mud?
My Saturn's speedometer shows a top speed of 130 mph, although I have never reached that speed. But my tires, I believe, are only rated for sustained speeds of 84 mph.