askST: Why do trains go slower when it rains?

Reader Gabriel Tham wrote in to ask: "Why do MRT trains have to move slower when it rains? Road users drive slower because of safety reasons, but why trains? "

Senior transport correspondent Christopher Tan answered.

MRT trains go slower when it rains because of safety reasons, too.

The weather, however, affects trains on surface lines only. This is because when it rains, the tracks get wet. And trains will require a longer braking distance when the tracks are wet - just like road vehicles on wet roads. To compensate for the longer stopping distance, trains go slower.

The rain does not affect underground lines. But operators may at their discretion adjust scheduling of these lines to cater to the slower arrivals of surface trains at interchange stations on wet days.

The train network is like a giant living organism - what happens to one part will have an effect - no matter how small - on other parts. The commuter does not always feel this ripple effect unless it is major.

More askST stories here.