The impact of a pole by a TTC bus in Toronto yesterday afternoon reflects the general weakness of bus structures. The Humboldt Broncos bus crash in Saskatchewan earlier this year demonstrated how catestrophic bus crashes can be because of the potentially large number of occupants  who are not afforded the general safety protections available in modern passenger cars and light trucks.

Generally, buses are much more massive than typical passenger cars, Pick-up trucks or passenger vans. As such, as they gain speed, they possess a much larger kinetic energy. When an impact occurs that kinetic energy needs to be disposed of, or dissipated, in order for the bus to stop. In the Toronto crash some of the kinetic energy of the bus might have been lost during any pre-impact braking and swerving by the bus driver in order to evade the pedestrian that reportedly walked/run onto the road. Given the typical city speeds of such buses we would not be looking at a high-speed event even if no pre-crash braking occurred. But even though a relatively low speed was involved when the bus struck the pole, there would still be much more kinetic energy simply because of the large mass of the bus.

Looking at the bus damage, there was a typical, narrow loading of its structure due to the narrowness of the pole. So we would expect the pole to penetrate the bus to some degree. On the other hand, the pole was merely bent slightly from its vertical position and this also demonstrates the relatively small force that was applied. Issac Newton’s Third Law demonstrated that, for every action there is an equal and opposite reaction. Therefore the force on the pole was equal to the force on the bus. So we can generally conclude that the force exerted on the bus was “not large”. Yet there was substantial crush and intrusion into the interior.

It is not meant to single out the particular manufacturer of the TTC. However, in general, it needs to be appreciated that bus structures are generally weak in proportion to their mass. This results in substantial disintegrations, separations and failures of the structure whenever a bus crash of substantial speed is involved. This is not good news when combined with the possibility that a bus could be loaded with several dozen passengers. This is not an easy problem to solve and therefore it is rarely discussed. However the tragic results of collisons such as the one involving the Humboldt Broncos is a reminder that this problem needs to be at the forefront of the public asking officials what improvements can be reasonably made.