Split platform

A split platform is a station that has a platform for each track, split onto two or more levels. This configuration allows a narrower station plan (or footprint) horizontally, at the expense of a deeper (or higher) vertical elevation, because sets of tracks and platforms are stacked above each other. Where two rails lines cross or run parallel for a time, split platforms are sometimes used in a hybrid arrangement that allows for convenient cross-platform interchange between trains running in the same general direction.

On the London Underground, to minimise the risk of subsidence, the tunnel alignments largely followed the roads on the surface and avoided passing under buildings. If a road was too narrow to allow the construction of side-by-side tunnels, they would be aligned one above the other, so that a number of stations have platforms at different levels.

This setup is not common in North American railroad stations, but is found in places in Europe such as the London Underground on the deep tube lines, namely the Bakerloo, Central, Jubilee, Northern and Piccadilly lines.

Examples of split platform layout in the United States are Rosslyn on the Washington Metro's Blue and Orange Lines; Pentagon on the Washington Metro's Blue and Yellow Lines; and Harvard and Porter stations on the Boston-Cambridge MBTA Red Line. Split platforms are also at downtown Oakland, California on BART's 12th and 19th Street, and at Los Angeles Metro Rail's Wilshire/Vermont. MARTA's Ashby station uses the configuration to separate the eastbound and westbound platforms. A similar configuration was once planned for downtown San Francisco stations, but the lower level was used for San Francisco Municipal Railroad trains.

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