Years after Wi-Fi connections have become ubiquitous on university campuses, in coffee shops, and in public buildings, the ability to connect to the Internet during a morning commute is still an exercise in frustration for many Americans.

Yesterday the Metropolitan Transportation Authority (MTA) in New York City said it was moving forward with a pilot program to bring Wi-Fi to customers in select subway stations. While promising, the initial rollout includes only a few stations, and it’s coming years after Wi-Fi has become commonplace.

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This isn’t the case everywhere. In 2005, for example, Wi-Fi service was added to the train connecting London and Brighton in the U.K., with users able to access 802.11b connections within the train’s cars. More than five years later, Charing Cross became the first London Underground station to receive Wi-Fi within London’s tube system, and reports say Wi-Fi will be widespread in the system by 2012.

While commuters in many cities overseas have some kind of connectivity (in stations, on trains, or both), the U.S. hasn’t been so lucky. Even in the highly connected San Francisco Bay Area, underground Wi-Fi in BART stations is still a thing of the future. Without specially installed base stations, neither Wi-Fi-equipped laptops or smartphones can penetrate the layers of metal, stone, and concrete that can isolate a train tunnel from the outside world.

Key Decision: Wi-Fi or 3G?
Historically, connectivity has equaled Wi-Fi, either via a dongle or built-in wireless chipset. Outside of 802.11n, however, Wi-Fi connections are fairly short-range, and, on a moving train, fail altogether without some sort of wireless backhaul. In stations, though, while commuters wait for a train, there can be a high-speed pipe through which a laptop can quickly download accumulated email.

In recent years, however, cellular connectivity has dramatically improved in both coverage and throughput, leaving operators of municipal transportation systems with something of a quandary: should they build in dedicated Wi-Fi connections, or place the burden on existing 3G networks? With more and more users connecting via 3G services, especially with the rollout of LTE services from Verizon and others, it appears that cities may be favoring the latter. (Of course, that market has become even more interesting with the proposed acquisition of T-Mobile via AT&T).

In cities like Chicago and Seattle, whose transportation systems are typically above ground, city planners haven’t been forced to make decisions about which technology to favor. (Seattle hasn’t placed Wi-Fi hotspots near its monorail stations, for example, although it has placed free municipal Wi-Fi in its Columbia City and the University District business districts, and the City Hall lobby area.)

In places like New York City, however, with the largest subway system in the United States, Washington D.C., and even the Bay Area, where the transbay BART tunnel and several San Francisco stations are all underground, the decision to favor either 3G or Wi-Fi, or both, becomes more pronounced.

Below, we’ve taken a look at five major cities within the U.S., with an eye toward what sort of connectivity you can and may expect in the future. Hit the “Next” link below to see the state of wireless connectivity in the subways of Boston, Chicago, and New York City.