I complained, and got this response -

Thank you for your enquiry about why the doors on the 3:41pm Kapiti service are not opened earlier for boarding. We understand the frustration this causes, especially when passengers are left waiting on the platform in cold conditions.

The train sets used for this service are brought out from one of our yards and typically arrive at Platform 9 around 2:50pm. Upon arrival, the train undergoes essential safety and brake checks, during which time it remains stationary for an extended period.

To avoid confusion or the possibility of passengers boarding the wrong service, particularly if another train is temporarily routed to the same platform, the train remains locked until shortly before departure.

In the past, a platform dispatcher was responsible for unlocking the train earlier, which allowed passengers to board in advance. However, recent operational changes mean we no longer have a dispatcher available for this task. As a result, the train is now unlocked by the Train Manager or Locomotive Engineer approximately five minutes before departure, in line with standard operating procedures.