Hey, what if cars were built so that they had lots of low end to get up to speed quickly but the top end speed was barely over the highway speed limit?
Almost seems like a good idea but... While speed must always be a factor in a crash (2 parked cars will never hit each other, at least one must be moving), speed being the cause of a crash is a much much rarer thing. Speed above what is safe for the conditions might cause a lot more, but there are many many many many roads and many many many many times when the legal speed is way above the safe speed.
Come over here and I'll show you roads where averaging 1/4 of the legal limit will get you killed, no ifs buts or maybes.
Teach people to drive at a speed safe for the conditions, and if conditions change to change their speed appropriately. Teach them that regardless of what they drive, where they drive, or who else is on the roads around them, the driver is responsible for getting their vehicle to its destination safely, and that means being alert because (as a long running ad campaign in NZ says) "other people make mistakes". If you can act to prevent a crash and don't, then even if the other person was legally wrong you are at fault. Teach people to do this and watch accident rates plummet.
PS My bike, when she runs, can do double the legal speed. Difference between 80kph and 140kph (automatic loss of license) is a slight twist of the wrist and a few seconds (not that I've ever gone that fast, HONEST!). I don't drive at speeds faster than is safe because 1) I am in control of myself, 2) I am in control of my vehicle, and 3) I've done every bit of extra training I can afford and 4) I get out and PRACTICE things like emergency braking - I know how my bike will perform in an emergency and I know how to counter any quirks. I do the same with the cage, I know it has a slight pull to the left under very hard braking and I know what is needed to counter it. Practice makes this automatic so I don't need to think "oh hell my car is changing direction what do I do" I can instead focus on "where is the gap I need to get through to survive" and avoid whatever else I need to avoid.