Rail commuters in Auckland and Wellington are being urged to check timetables before heading back to work on Tuesday.
KiwiRail has used the traditional holiday lull in commuter traffic to carry out an upgrade of train services in both cities.
KiwiRail spokesperson Ruth Larsen says the upgrade is almost complete but work will continue in Wellington until Wednesday, and in Auckland until 18 January.
Buses will replace trains as needed.
Mr Larsen says the holiday timetable is slightly different to the normal timetable and commuters should check the TransMetro or Metlink websites to make sure they know where and when services are running.
Meanwhile, rail network maintenance agency Ontrack says a signaling fault that caused train delays in the lower North Island on Monday has been fixed.
It says the fault caused problems from Marton south and was affecting mainly Tranz Metro trains.
Extra buses were put on to replace trains on several affected lines.
