Final answer:
When passing, you close in on an approaching vehicle at twice your speed if it's stationary; with both vehicles moving, the closing rate can exceed this, requiring careful calculation for safe passing.
Step-by-step explanation:
When passing a vehicle while driving, you are closing the gap between you and the approaching vehicle at twice your own rate of speed if the other vehicle is stationary. If the oncoming vehicle is also moving, then the rate at which you close the gap could be even greater, potentially more than twice your speed, depending on the speed differential. It's important to account for this relative motion especially in head-on passing situations to ensure safety and to avoid miscalculating the available time and distance required to pass safely.