Final answer:
One should wait until a car is at least 56 meters or approximately 16 car lengths away before crossing the road, given the average walking speed and the speed limit of 60 km/hr for vehicles.
Step-by-step explanation:
When considering the safety of crossing a road in the context of oncoming traffic, it's important to calculate the distance that must be clear before you decide it's safe to cross. Given the speed limit of 60 km/hr, which translates to 16.67 meters per second, and knowing that you need to be able to walk 4 meters to cross safely, we can calculate the necessary distance for a car to be from you before initiating the crossing.
To safely cross, you should be 4 meters away from the side of the road before a car reaches you. If you can walk at a speed of about 1.2 meters per second (average walking speed), it will take you approximately 3.33 seconds to cross 4 meters. During those 3.33 seconds, a car traveling at 16.67 meters per second will cover a distance of approximately 55.56 meters. To ensure safety, rounding this up is reasonable, so it is advisable to wait until the car is at least 56 meters away.
Given that the average car length is 3.5 meters, this distance corresponds to about 16 car lengths (56 divided by 3.5). This means that you should not start to cross the road if an oncoming car is less than 16 car lengths away. It is always better to err on the side of caution when it comes to road safety.