How does crash barriers and road surface technology help road safety?

Answer 1

When a vehicle is traveling, it's speed and mass constitute kinetic energy, called momentum. During an accident all of this energy has to be disipated to zero in a very short time. If this happens instantaneously, like when something falls from a tall building and hits the ground, the impact force is maximum and does the most amount of damage to the object. If the duration time of the impact can be extended by dissipating the energy over a distance, then much of the energy can be utilized to deform other materials, and the remaining force imparted to a cars occupants decreased.
Car designers use crumple zones to control deformation and maximize energy absorption during an accident, along with designing the passenger compartment to be strong and resist crushing in order to best protect the occupants. Crash barriers along the road work in a similar way, they absorb energy as they are deformed over a distance, and this is better than having this energy absorbed by the car. An example of a crash barrier is a series of water filled barrels. As they are smashed by the car the water inside shoots in all directions, and it takes energy to displace the water this way.
Some examples of road surface technology that improves safety are: (1) a slight crest to the road to cause rain water to run off towards the side of the road, which avoids puddles and cars hydroplaning; (2) grooves cut into the road surface to channel water away, used on cement highways because cement can better keep the grooves compared to macadam, and it is more important on highways where speeds are faster; (3) rumble strips at the edge of a highway causes a loud noise that wakes up drifting drivers; (4) the raised pavement markers between lanes serve a similar purpose and are many times also reflective (the domed shaped ones are sometimes called Botts Dots after Elbert Botts who invented them); (5) then there's the good old speed bumps used to slow cars in areas of pedestrian traffic.