I feel your pain. There's just no way I would do this either. I wonder if the other parent(s) was even aware or understood these details. I would not want to drive 90 minutes for a concert and my answer would be "no." If the other parent was okay with this and they wish to drive, yay, you have a ride. When plans change, sorry. You need to plan better. I would be upset with the other parent for agreeing and then bailing, but it's really not up to you be the one to rescue either. Especially if this is a continued problem. I have made longer trips and carpooled and waited and picked up and dropped off. This has been in communication with the other parents, and I have found on the rare occasion the other parent wasn't entirely clear on what the plan was either. We have made it work, but it is an important part of the learning process to make sure these plans can work and the transportation, time, money, other people's lives and schedules, not just that someone would be available at the last minute.
You are on the right tracks and fine with saying no. My oldest is 14, and I haven't really gotten into a lot of this teenage stuff just yet, but I have had tasters, and I'm glad to learn from others' experiences.