Final answer:
The exact speed at which three out of four crashes happen is not provided, but research and safety campaigns suggest that many occur under 40 miles per hour. Roads safety education emphasizes cautious driving at all speeds to prevent accidents, and crash test scenarios, like those with dummies at 35 miles per hour, help study the potential for injury.
Step-by-step explanation:
The statement 'Three out of four crashes happen at a speed of __________ miles per hour or less' does not have enough information provided to fill in the blank accurately with a specific number. However, for the purpose of road safety education, it is often cited that many crashes occur at lower speeds. For example, according to some safety campaigns and research, a significant number of crashes occur at speeds under 40 miles per hour. In the context of the driving examples provided, it is implied that even at a speed limit of thirty-five miles per hour, as mentioned in the scenario with Peter, driving cautiously is important to prevent accidents.
In another example, cars with dummies were crashed into a wall at a speed of 35 miles per hour to assess head injury potential, illustrating that crash tests are often conducted at speeds that are considered common in real-world collisions. Driver error, a significant factor in crashes, can happen at any speed, but the consequences are usually less severe at lower speeds. Understanding the impact of speed on traffic collisions is important for drivers to make safer choices on the road.