Next time you reach a signalized intersection, while you are waiting for the beg button to supply you with permission to cross, check out the base of the pole holding up that signal. The pole looks like it is attached to the ground, but if you look closely, you will see that it’s not. At least not directly.
The pole will have a series of bolts—they are shear pins—that attach it to the base buried in the ground. Those bolts are designed to give way, to shear off, if the pole is struck with enough force. This is done because cars leave the street surface with such frequency, and with such violent force, that many drivers were being injured and killed hitting poles that did not yield.
Ponder this the next time you are standing at the signal, waiting to cross. The next time you are standing in space that licensed professionals have recognized is so dangerous that the extra effort and expense to absorb that violent force is justified. To protect those in vehicles. To save the lives of those that drive their cars off of the street surface. The street surface you are standing next to.
Standing right where those out-of-control vehicles are expected to go.
It is worth contrasting this with the way median barriers are used on highways. On a highway, vehicles are traveling with great kinetic force in opposite directions. Sometimes they are separated by paint and sometimes by a ditch, but increasingly transportation professionals find it beneficial to install some type of barrier between the lanes of travel.
It might be a metal fence. It might be a concrete wall. Great care has been taken to test the ability of these barriers to resist the force of a colliding vehicle.
This seems very logical. And prudent. A vehicle leaving the roadway has the potential to cause traumatic injury to anyone in a vehicle in an opposing lane. It is better to stop that projectile from inflicting such damage, despite the violence this will do to the driver of the errant vehicle.
Construction workers doing maintenance on a roadway rightly demand concrete barriers between them and the traffic flowing next to them. Those who design maintenance projects acquiesce to that demand, not just because they want the construction to proceed but because they understand that it is really dangerous to have humans standing near traffic flowing even at moderate speeds.
The concrete barriers do not have a breakaway design. There are no shear pins to absorb the kinetic energy of an errant vehicle. A driver who loses control in a construction zone is going to feel the brutal consequences of that mistake. The construction worker will not.