Selective door operation

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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.