I'm relatively new to New York and ride the subway every day. When I'm on the above-ground lines I notice another "fourth" rail in between the two running rails that doesn't look like it is used, but is securely tied down. Sometimes there's even a fifth rail, also in the middle. Usually this rail doesn't run continuously and it occasionally curves or has other oddities. What is this fourth rail for? [more inside]
posted by pithy comment on Mar 23, 2007 - 15 answers