Generally, there are 2 forces at play dictating how fast people will go on a given road. The probability of getting caught speeding is one, the other is the perceived safety of going fast. The issue most American roads have is that they are built extremely wide, with even more open space on either side of the road, so people are comfortable gunning it. Speed limits only matter insomuch as they adjust the perceived probability of being pulled over.

Our highways also train you that speed limit are complete bullshit. On an 8 lane, divided highway, with nothing but empty field or protective barriers on either side, 60 mph is comically low. That's how you end up with absurdities like it often being unavoidably illegal to drive on 680 in the Bay Area: either you're speeding, or you're obstructing traffic, both of which carry a fine.

IMO, the correct answer is to raise the speed limit of surface streets that already double as psuedo-highways (looking at you, San Jose), strictly enforce speed limits on surface streets, and then completely eliminate speed limits on the freeways.