Letters | Mind the history and geometry of MTR platform gaps

Readers discuss the curved station platforms along the East Rail line, the delay in installing platform screen doors, and economic concerns over the artificial islands project

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A view of University MTR Station. Photo: Winson Wong

Published: 11:30am, 10 Apr 2023

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I refer to the letter, “MTR platform gaps must be addressed” (April 3). Unfortunately, history and geometry are against your correspondents.

The fault lies primarily with the private joint venture that financed the construction of the British Section of the KCR, which opened in 1910 and is now the East Rail line. “Best value for money” dictated that the railway wend its way around topographic obstructions, wholly ignorant of future plans to convert it into a metropolitan railway with new stations serving undreamed-of population centres. Irredeemably, some stations – including University and Kowloon Tong – had to be on a curve.

As for the geometry, draw a chord to a part of a circle. The length of the chord represents the length of a rigid railway carriage; the curve is the platform edge. The maximum distance, at right angles, from the chord to the circle indicates the maximum platform gap for a curve of that radius and a carriage of that length. This is an unassailable fact for a platform on a curve, and prevents carriages colliding with platforms.

Faced with reality, the MTR Corporation can only advertise and exhort passengers to “mind the gap”.

Finally, the comment about “pressure mats along the tracks to prevent a train from running over a passenger falling into the gap” must be addressed. There must be a train already standing at the platform for a gap to exist between platform and carriage – a standing train cannot run over a passenger on the track.