Most of the rail network in Wellington is shut this weekend while the lines signalling system is upgraded.
Lines are closed from 4am on Saturday until 4am on Monday.
Buses will run in place of rail services connecting Hutt Valley, Johnsonville, Paraparaumu and Wairarapa.
KiwiRail says the computerisation of the system was planned 15 months ago and is not related to signalling problems that caused major disruptions to commuter journeys last month.
Project director David Gordon says he does not anticipate any teething problems with the new system.
Passengers using replacement buses will be charged the full train fare.