“Hey, buddy, you need a limo into the city? Seventy bucks.”Arriving at a strange airport can be unnerving, especially when some unsavory character with a chauffeur cap sidles up to you at the baggage carousel, looks furtively around the terminal, and whispers something like that.Most of us are smart enough to give guys like him a wide berth and look for safer, more legitimate means of transportation. But that’s also when many travelers throw in the towel and head for the nearest taxi rank. “It may be a lot more expensive to take a cab,” they say to themselves, “but at least it will get me to my hotel fast.” Fast? Sometimes yes, sometimes no. Expensive? Usually. That’s why conscientious travelers—at least, those not schlepping a lot of baggage—always consider whether public transit is a practical alternative.And sometimes it is. Coming into Chicago from O’Hare? A taxi to the Loop is going to set you back as much as $40 and take up to 30 minutes. Hop on the CTA Blue Line train, though, and it’s just $2.25—and the scheduled trip is only 10 minutes longer. Newark to New York City can be an even bigger bargain, especially if you’re traveling alone. For $15, the AirTrain links up with New Jersey Transit’s trains for the 30-minute trip. A taxi shaves just five minutes off that time, and costs $55. (Of course, that does get you door-to-door service.)Internationally, nothing makes an air traveler feel more like a local than taking public transportation to the city and avoiding long and expensive taxi rides. That’s especially true in Tokyo , where a taxi from Narita costs an eye-popping $220. Our suggestion: take the plush Narita Express, where a ticket is less than $35. And in Shanghai , skip the 45-minute taxi trip. The ridiculously fast magnetic levitation train is a thrill ride in itself, whisking you downtown in just eight minutes flat.No matter which city you’re visiting, you can check the air-rail service, where available, at Airport Railways of the World . Still, of course, public transportation isn’t always the right choice, so decide for yourself if the convenience of a taxi outweighs the additional cost.Our opinion? It rarely does.