Dollar - Shuttle buses at LAX

Back in August I waited 20 minutes outside the UA terminal for a shuttle bus. This past Friday night, I gave up on Dollar after waiting another 20 minutes or so for a shuttle. I jumped on an Avis bus and rented from them. What is with the shuttles at LAX?

I've only rented from Dollar LAX once, but I don't recall having to wait too long for the shuttle. (It does seem like that the National/Alamo buses come around every 30 seconds, though--way more than pretty much everyone else's buses.)

This past weekend I had the opposite, Waited forever for Avis while had 4 of everybody else