The Oakland Wye is an underground junction in downtown Oakland serving the Bay Area Rapid Transit (BART) system, where trains can switch between (a) the northbound Richmond or Pittsburg/Bay Point lines (first station: 12th Street/Oakland City Center, underground), (b) the westbound San Francisco lines (first station: West Oakland, elevated) , and (c) the southbound Fremont or Dublin/Pleasanton lines (first station: Lake Merritt, underground). The Oakland Wye has been described as one of the central and most complex part of the BART system, and is a speed bottleneck for the whole system because all BART trains pass through it.