I had my second rental with Avis at IAD last week and saw how they handled hiccups in the process. When the bus let me out, my car was there right in front of me, but unfortunately by the time got to the exit there was a line of about a dozen cars waiting to check out through the one gate. Apparently someone had trouble making the left turn out of the rental lot (some bad traffic engineering that Avis shares with Hertz next door) and hung up everyone behind them. A bunch of Avis people came out (some uniformed, some back office) and started collecting drivers licenses and contracts and got everyone cleared to just drive well before they got to the gate, so once things started moving again, it was a quick exit.