>For example, adding some barriers that obstruct sight
This sounds like a recipe to increase accidents, just saying.
Experience shows they're just the opposite.
The point is not to have much of the environment hidden from sight. The point is to prevent the 'All I see is open road' feeling. On a slightly too simple note, the point is to make you feel like you need to be more careful without actually adding a lot of risk.
One might say the current road design makes roads feel so safe that the actual safety benefits get canceled out by changed behaviour.
Adding some trees and shrubbery between the road and the sidewalk also does a lot. Because sidewalks next to a road visually widen the road. This has the added benefit of making pedestrians feel a lot safer. No-one likes walking 2 meters next to cars driving at near-highway speeds.