The easiest option is to just use public transportation. If you must use cabs, then I could never suggest NOT using a car seat. It may be perfectly legal not to use one, but that doesnt make it safe. Unless you'd be ok holding your LO on your lap driving around your own town, then you shouldnt do it anywhere else. It's not convenient to carry around a seat, but safety trumps convenience. Like I said, public transportation is the way to go. Most cities have buses which wont need a car seat because they're designed with compartmentalization for crashes and not the same as a passenger vehicle. Trains are also safe without car seats. I'd rather walk 20 blocks than take the risk of not having my LO properly secured in the car.