page_title: Green Line (MBTA)
section_title: Operations and signalling
hierarchical_section_title: Green Line (MBTA) / Operations and signalling
caption_attribution_description: Type 8 trolley #3835 at headed outbound at Newton Highlands station. The historic station building is to the right background. This is an image of a place or building that is listed on the National Register of Historic Places in the United States of America. Its reference number is 76002137
context_page_description: The Green Line is a light rail system run by the Massachusetts Bay Transportation Authority (MBTA) in the Boston, Massachusetts, metropolitan area. It is the oldest Boston rapid transit line, and with tunnel sections dating from 1897, the oldest in America. It runs as a deep-level subway through downtown Boston, and on the surface into inner suburbs via four branches on several radial boulevards. With an average daily weekday ridership of 152,200 in 2019, it is the second most heavily used light rail system in the country. The line was assigned the green color in 1967 during a systemwide rebranding because several branches pass through sections of the Emerald Necklace of Boston.
  The four branches are the remnants of a large streetcar system, which began in 1856 with the Cambridge Horse Railroad and was consolidated into the Boston Elevated Railway several decades later. The branches all travel downtown through the Tremont Street subway, the oldest subway tunnel in North America. The Tremont Street subway opened its first section on September 1, 1897, to take streetcars off overcrowded downtown streets; it was extended five times over the next five decades.
context_section_description: Unlike the MBTA heavy rail subway lines, the Green Line has only limited central control and monitoring. This also means that it has lagged behind the other three rail lines in the availability of countdown signs and "next train" arrival information.
  The line is signalled with advisory wayside signals, except on surface portions in street medians or in-street running. Wayside signal territory stretches from Lechmere to the surface portals at Kenmore, and along the entire length of the D–Riverside branch. There are no automatic protection devices, but the cars have track brakes, giving the ability to stop quickly under control of the operator. Interlockings are controlled through a wayside Automatic Vehicle Identification (AVI) system that relies on the operator properly entering the destination manually on a roto-wheel in the train cab at the beginning of a run.
  The line is monitored from the Operations Control Center (OCC). Responsibility for controlling service is shared by the control room and field personnel along the right of way. Track circuit and signal indications are not transmitted to the operational personnel sites. In lieu of track circuit indications, the AVI system is displayed in the control room to provide a periodic update to train position wherever AVI detectors exist. The AVI system user interface was solely text based until the current control room was opened, in which a new schematic display based on AVI data was instituted. Track circuit indications are available digitally in signal houses at the Park Street interlocking, at the new North Station interlocking, and at the new Kenmore interlocking, but are not transmitted to OCC. In January 2013, the MBTA announced plans to add full vehicle location tracking on the Green Line for countdown signs and smartphone applications, including using AVI data in the tunnels and GPS receivers on the surface lines. The first real-time data—location data on the surface lines—became available in October 2014. Full tracking was expected by early 2015.
  As of 2020, the MBTA typically runs two-car trains on weekdays, with one-car trains used at some times on weekends. The last scheduled use of one-car trains on weekdays was in March 2007.
  Three-car trains were added on the B and D branches in 2010 – their first use since 2005 – and a four-car train was tested in April 2011. In March 2011, the number of three-car trains was substantially increased, including use on the E Branch. However, three-car trains suffered from reliability problems and slow boarding. The use of three-car trains ended in March 2016.
caption: Trains on the D branch operate using wayside signals.
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