In what situation is a personal auto policy considered excess regarding liability coverage?

A personal auto policy is considered excess regarding liability coverage when it's used to augment other forms of insurance that already provide primary coverage in specific situations. In the context of the given choices, when driving a vehicle that is in a garage, there may already be other insurance policies in effect that take precedence in case of an incident.

For example, if an accident occurs while the vehicle is parked in a garage and the garage owner's policy or another primary coverage applies, the personal auto policy would serve as excess coverage, meaning it kicks in only after the limits of the primary coverage have been exhausted. This situation typically reflects scenarios where other insurance options are available to cover the loss before the personal auto policy is utilized.

In contrast, the other situations don’t typically lead to the personal auto policy being treated as excess. For instance, using the vehicle for commercial purposes could fall under specific business insurance rather than merely being excess; being parked at home generally doesn't involve a risk layering scenario that necessitates an excess coverage application; and driving under the influence raises different liability questions but isn't specifically related to excess coverage under a personal auto policy.