There is another way: make the road feel fast. Thankfully it doesn't need to be via bad road surfaces or horrible things like speed bumps that only encourage boy racers and reward large vehicles, making the road narrower with high kerbs or other physical obstacles force drivers to drive slowly and pay attention, otherwise they'll physically damage their vehicle. In a way it evens the playing field, currently cars can kill you, but they are untouchable, there are no consequences for speeding or being distracted. The main downside I can think of is the route becomes difficult for emergency vehicles to use, but with the saved space there could be a dedicated lane for public vehicles.

Ironically, the lower you are to the ground, the faster it feels - everyone should drive a sports car!

(conversely, I drive a motorcycle sometimes which puts my head at or just over roof height of most cars, it makes 80 km/h not feel as fast. Mind you, the added road overview also helps)

Anyway. Narrow / winding roads and speed bumps will definitely make you want to drive slower. We have 'cars are guests' roads inside cities too, which are roads designed and coloured like bike paths (= red asphalt).

But the opposite is also true; I got a speeding ticket once, the road was a 4 lane, separated directions asphalt ring road... but the speed limit was 50 km/h.

Or consider the width of the road...