Which of these factors does NOT affect the braking distance?

The factor that does not affect braking distance is engine horsepower. Braking distance is primarily influenced by the dynamics of stopping the vehicle, which are closely related to vehicle speed, the condition of the road surface (which can include incline), and the driver's ability to react quickly—essentially their alertness and readiness to respond in an emergency situation.

Engine horsepower refers to the power output of the vehicle's engine and plays a significant role in determining acceleration and overall vehicle performance. However, it does not directly impact how quickly or efficiently a vehicle can come to a stop once the brakes are applied. Instead, factors such as road conditions, vehicle speed, and the driver's attentiveness directly influence the distance required to stop safely. Thus, while horsepower may contribute to how fast a vehicle can drive, it does not determine how effectively it can brake.