CA and US law require car seats for a 6-month old child. But as far as I can tell, that doesn't really apply to shuttle buses. We've taken our baby on plenty of airport, hotel and car rental shuttles and nary a one said anything about a car seat.

I think car seats are required in taxis though. Some taxis actually have a loaner in the trunk.

But that's all moot:
http://www.travelodgesfairport.com
Cynthia at the front desk says no car seat required on the shuttle buses (which run 24 hours to/from the airport).