If you are taking a taxi, then you will have to provide your own car seat. The current law (just changed on 1/1/2012) is that children under age 8 or 49" must be secured in either a car or booster, AND must be in the back seat.
Larger vehicles like passenger buses do not require this, but shuttles and taxis will require your child be secured. If you take a shuttle, some will let you call ahead and request that they bring a car seat (possibly at an additional fee), but you'll be better off bringing your own if you plan on using taxis.