Final answer:
At 40 mph, the rule of thumb for driving on wet pavement is to keep at least four car lengths between vehicles. Safety distance while crossing the road is dependent on walking speed, the speed of oncoming vehicles, and road conditions.
Step-by-step explanation:
When driving on wet pavement, a good rule of thumb is to maintain at least one car length for every 10 mph of speed. Therefore, at 40 mph, you should keep at least four car lengths between you and the vehicle you are following. However, this question does not have enough information to properly determine the safe following distance on wet pavement, as factors such as visibility, driver reaction time, and vehicle braking efficiency would also need to be considered. With reference to the given information, the stopping distance on wet pavement includes both the distance traveled during the driver's reaction time and the braking distance. With these variables, a safe distance cannot be accurately given without additional context such as the vehicle's braking capabilities or the driver's attentiveness.
If you are on foot and see a car driving toward you at a speed where it will take less time to reach you than it takes for you to cross the road, it is not safe to proceed. A safe distance to cross would be one that allows you enough time to clear the car's path before it reaches you. The recommended distance would vary based on factors like the car's speed, your walking speed, road conditions, and traffic laws.