Neighborhood distribution lines can also sometimes produce significant magnetic fields, depending on the amount of current they carry. In general, the strongest EMFs around the outside of a substation come from the power lines entering and leaving the station. The strength of the EMFs from transformers decreases rapidly with increasing distance. Beyond the substation fence, the EMFs produced by the equipment within the station are typically indistinguishable from background levels. Alternators can create EMFs, but not at 60 Hz.
Most trains are diesel-powered.
Some electrically powered trains operate on AC, such as the Baltimore-Washington commuter train. Other trains, such as the Washington D.C. Metro and the San Francisco Bay Area Rapid Transit, run on DC, but even these trains are not free of AC fields. Areas of strong AC magnetic fields have been measured on the Washington Metro close to the floor, presumably near equipment located underneath some subway cars. Train motors and other equipment can create alternating fields at higher than 60-Hz frequencies. In addition to sources of magnetic field exposure from the train itself, train passengers are exposed to magnetic fields from sources the train passes on its route.