What defines a temporary substitute vehicle?

A temporary substitute vehicle is typically defined as a vehicle used when the insured's own vehicle is not accessible for some reason. This might occur due to repair, servicing, or any situation where the insured cannot use their primary vehicle. The usage of this substitute vehicle allows for continuity of transportation during the time the primary vehicle is unavailable.

In the context of the other options, while a vehicle owned by the insured that is being repaired suggests a similar scenario, it does not capture the essence of using a temporary vehicle due to lack of access. The second option refers to driving a vehicle when the insured vehicle is still available, which goes against the necessity of substituting due to inaccessibility. The rental car for a vacation implies a different context, where the vehicle is not substituting for an unavailable vehicle but is rather an additional vehicle for leisure purposes. Therefore, the definition that closely aligns with the intended meaning of a temporary substitute vehicle revolves around the inability to access the insured vehicle, thus validating the correctness of the chosen answer.