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.

They did try this approach. There's big concrete flower boxes in many places to create some artificial hindrances. It hinders your vision, causes people to swerve, it's annoying to give way. And worst of all: it slows people down for 2 seconds after which they just floor it.

Honestly it's already pretty narrow and crowded here. I'm a regular driver here (duh) and it honestly feels dumb to drive faster than 30 because a cyclist can pop out of every corner. It's crazy to me that people want to, and do drive faster than that. But here we are. People suck.

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...