Final answer:
The car on the right has the right of way at a 4-way stop when three vehicles arrive simultaneously; however, emergency situations may require flexible application of the rules.
Step-by-step explanation:
When three vehicles reach a 4-way stop at the same time, the rules of the road dictate that the car on the right has the right of way. This is a universally accepted traffic rule meant to control traffic safely at intersections without traffic lights or roundabouts. However, if one of the vehicles is in an emergency situation, such as a pregnant woman on the verge of delivery in the back seat, real-world judgment and exceptional circumstances could alter the standard rules. It is important to use common sense, courtesy, and caution in any driving situation, especially when dealing with exceptional cases like emergency medical situations or pedestrians trying to cross.