Collision severity is what causes injury and death. But how is that determined? Looking at damage alone can be deceptive.

A school bus collided with a tree on John Street in Stratford, Ontario on the morning of Thursday, November 2, 2023. Photos of the collision such as the one above were posted on Twitter by the Stratford Police Service showing the extensive damage to the bus. While the collision was of substantial severity it was reported that 12 students were on the bus when the impact occurred but none were injured. It often begs the question: why did so many occupants appear to have been uninjured when photos such as the one above show so much damage?

In truth, at the time that this collision was reported, it was only a few hours after it occurred. While some students may have been uninjured some may not exhibit symptoms from soft-tissue injuries sometimes until a delay of 48 hours. While paramedics may have examined the students and released them that may only mean that they did not require immediate transfer to a hospital. But soft tissue injuries are often difficult to detect especially after such a short time after an incident.

Yet many would look at the damage in the above photo and draw the conclusion that this was a massive collision because of all the visible damage. After all, persons may have seen impacts of cars striking trees where fatalities occurred and the amount of visible damage was certainly comparable. And this is a false assumption.

Visible damage is an indicator of the kinetic energy that was dissipated, or used up, in a crash. Kinetic energy exists because objects (i.e. masses) are in motion. Kinetic energy is a product of the velocity of the object as well as its mass (or “weight” for easier understanding although not technically correct). Two vehicles travelling at the same velocity may possess different quantities of kinetic energy because they may be of different masses. So a school bus, because it “weighs” so much more, will possess a lot more kinetic energy than a passenger car. When an impact occurs kinetic energy becomes dissipated in order to bring a vehicle to a halt. But a vehicle which is more massive, like a school bus, needs to get rid of a lot more kinetic energy to stop than a passenger car. So when a school bus strikes a tree it may cause more damage to itself, and to the tree, because it had to get rid of that extra kinetic energy. So this can be confusing to some. The logic is that more damage must mean higher severity and that is not always the case. You must consider mass before you come to a conclusion about collision severity.