Selective door operation (SDO), also known as selective door opening, is a mechanism employed primarily on trains (although buses with multiple doors also generally have this feature) that allows the driver or conductor/guard to open the doors of a train separately.
Selective Door Operation enables trains to call at a station where the platform is shorter than the train. Some doors can be prevented from opening to ensure that passengers do not disembark from any carriages not standing at the platform. The term Selective Door Operation is used mainly in the United Kingdom; some train operating companies used the term ‘Door De-Select’. A version of this is used in other countries and on other rail systems such as the London Underground.
In the UK various trains, either multiple units or coaches, have variations of the selective door operating system. This usually depends on what the specific train operating company and/or train leasing company required, either at time of purchase or a later modification to an existing train to keep up to date with regulations. Examples of these variations are as follows:[1]
Selective door operation is implemented at certain railway stations in the United States. In the New York City Subway, the 6+1⁄2-car-long platforms at 145th Street (and formerly the 5-car-long loop platforms at South Ferry) are too short to accommodate full-length trains of ten 51.4-foot-long (15.7 m) cars, so only the first five cars of the train opened their doors at these stations. Also at South Ferry, the inner platform's curves were so tight that only the inner doors of the cars were able to be opened. At Times Square on track 4 of the 42nd Street Shuttle, the original platform was so short that only the first door of the third car was allowed to open at the station. After a reconfiguration of the shuttle in 2021, it is now possible for an entire train to fit on track 4.
On the Staten Island Railway, the Richmond Valley station only allows for the first three cars to open, due to the short platforms which cannot fit four 75-foot-long (23 m) cars. In addition, the last car for St. George-bound trains do not open at Clifton, due to the wide space from trains caused by the platform's curvature. Before they were demolished in 2017, the Atlantic and Nassau stations only allowed the last car of a train to open its doors at the platforms.
In Boston, the boarding platform at the Bowdoin terminus of the MBTA Blue Line accommodates only four of the train's six cars; passengers must press buttons to open the doors. Similar selective door operation protocols are used on many commuter rail lines within the Northeast megalopolis since some commuter rail stations have platforms that are too short to accommodate longer trains.
In Seattle, the Satellite Transit System at Seattle-Tacoma International Airport uses selective door operation on the loop connecting the South Satellite (the airport's international concourse) with the airport's main terminal. Passengers on most international flights arrive at the South Satellite, where they are inspected by U.S. Customs and Border Protection officials; after clearing inspection, passengers have the option of waiting in line to be inspected by the Transportation Security Administration so that they may access the rear two cars and secure area of the airport (to catch a connecting flight) or directly boarding the first train car which transports them to the airport exit and the baggage claim area. The platform screen doors that provide access to the first car of the train do not open at the station serving Concourse B of the airport to prevent unscreened passengers from accessing the concourse.
In many NSW TrainLink stations in New South Wales, Australia, due to shorter platform length than trains, only selected doors will open. One example would be Wondabyne railway station or Zig Zag railway station, where the extremely short length of platform only allows rear door (next to crew cab) on the last carriage to be opened.
In New Zealand, “selective door opening” is used on the Wairarapa Connection commuter train, as the Maymorn railway station platform is not long enough to accommodate all the carriages, and Maymorn passengers are restricted to the first three carriages.
Most modern Selective Door Opening (SDO) systems receive their positioning data from the Global Positioning System (GPS). As the train arrives at a station, the GPS determines the location for the train's SDO control, which contains a database with a Unique Location Identifier (ULI) for each station. This then enables the correct number of coaches to be opened to suit the length of the platform. However this system is reliant on the train stopping in the correct position, since the SDO will authorise the doors to open as long as the train is within 300 metres of the station.[4] Depending on which system is in use, SDO may not prevent the doors from being opened where there is no platform if;
Selective Door Operation is different from Local Door Operation (LDO), which is used on many trains by train crew and other staff.
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