line has that express service. There are several common platform configurations: On a 2-track line, a station may have one center island platform used for trains in both directions, or 2 side platforms, one for a train in each direction. For a 3-track or 4-track line, local stops will have side platforms and the middle one or two tracks will not stop at the station. For most 3- or 4-track express stops, there will be two island platforms, one for the local and express in one direction, and another for the local and express in the other direction. Each island platform provides a cross-platform interchange between the local and express services. In a few cases, a 4-track station has an island platform for the center express tracks and two side platforms for the outside local tracks. This occurs only at three stations near major railway stations where the next station along the line is also an express station with the more common platform configuration. The purpose of splitting the platforms is to limit overcrowding by preventing cross-platform interchanges between local and express services. The oldest station to be built with this layout is the Atlantic Avenue–Barclays Center station on the IRT Eastern Parkway Line (), where the connection is to the Atlantic Terminal of the Long Island Rail Road, with an adjacent express station at Nevins Street. The layout also exists at 34th Street–Penn Station on both the IRT Broadway–Seventh Avenue Line () and IND Eighth Avenue Line (), with adjacent express stations at Times Square–42nd Street and 42nd Street–Port Authority Bus Terminal, where the connection is to Pennsylvania Station, one of the two major New York City railway stations. This does not occur with the connection to New York's other major station, Grand Central Terminal, at Grand Central on the IRT Lexington Avenue Line (), which has no adjacent express station. There is one notable 6-track local station, DeKalb Avenue on the BMT Fourth Avenue Line, where trains to or from the Manhattan Bridge either stop at the outer tracks of the island platforms () or pass through and bypass the station on the middle tracks ("bypass express tracks") (). Trains to or from the Montague Street Tunnel () stop across the platform from the respective outer track. Stations with two levels Some stations have two levels. The levels separate the platforms of different services and/or directions. For example: