Which factor does NOT affect high-speed collisions?

High-speed collisions are primarily influenced by factors directly related to the dynamics of a crash and the physics at play. The type of fuel used in a vehicle does not influence the severity of a collision or how it impacts the occupants during an accident. Instead, factors like the force of impact, how well vehicles and their safety features protect occupants, and road conditions play crucial roles.

The ability of vehicles and restraints to protect occupants directly relates to safety features like airbags and seatbelts, which can significantly mitigate injury during a collision. The force of impact is fundamental since it is determined by the speed of the vehicles involved and their mass, thereby directly affecting the severity of injuries in an accident. Road conditions also have a major impact on vehicle control and stopping distance, which can influence crash outcomes. Therefore, the type of fuel does not contribute to these dynamics, making it the factor that does not affect high-speed collisions.