I thought this article was pretty interesting. Makes me wonder why though, since the shortness of most trips and potential disruptions make such a service questionable.

Merely hours after hearing that a contactless payment trial was going live on San Francisco's BART, along comes word that a test of a slightly different nature was also underway on the very same public transportation system. Reportedly, a recent Wi-Fi Rail installation on a select stretch of track proved that WiFi could be delivered to passengers at around 15Mbps -- up and down -- and if things go smoothly, the firm hopes to get its technology onto all sorts of rail systems across the globe. Unfortunately, there doesn't look to be any firm plans for the trial to stick on BART, but who knows, keep on refreshing that nearby network list on the morning commute and you might just get lucky.