Final answer:
The three-second rule is true for determining a safe following distance in driving, which accounts for vehicle speed, reaction time, and road conditions, ensuring sufficient space for stopping and reacting to road hazards.
Step-by-step explanation:
The statement that the three-second rule helps the driver determine a safe following distance is true. This rule suggests that a driver should stay at least three seconds behind any vehicle that is directly in front of the driver's vehicle. It is a useful way to ensure enough space for braking and reacting to unexpected situations on the road. Road conditions, driver reaction time, and vehicle speed are critical factors that influence braking distance as well as the total stopping distance. In dry conditions, for example, a car traveling at 30.0 m/s (around 108 km/h) will require a substantial distance to come to a complete stop once the driver reacts to a hazard. These principles are important when considering road safety and are directly related to understanding how far away a car must be before it's safe to cross the road.
In terms of determining how many car-lengths is needed for a safe following distance, it's dependent on speed and road conditions. Given that the average car length is about 3.5 meters, a three-second following distance would be many car lengths at highway speeds. However, in terms of crossing the road safely, you need to be able to walk at least 4 meters, further than the width of a car, before that car reaches you, especially if the speed limit is 60 km/h (as is typical in towns and cities).