A new third main line into Wellington Railway Station was successfully brought into service this morning.

KiwiRail completed the final changes to railway signalling over the weekend to enable the new line to be gradually brought into operation from today.

Wellington rail upgrade Project Director David Gordon said following a relatively smooth morning, the team felt positive about how the new line would operate in future.

"It is still early stages but we feel good about how things went this morning. There is an inevitable bedding-in process as we introduce new infrastructure so we'll be watching closely how things go over the coming weeks," David Gordon said.

"Our passengers are unlikely to notice any immediate benefit but over time they may realise that their trains have to wait less often at the entrance to Wellington Station."

Many train services from the Hutt Valley travelled on the new line this morning and there were a number of occasions when the new line was used with two trains coming in at the same time, when previously one would have waited to take its turn in the queue.

The line is designed to reduce congestion at a known bottleneck in the rail system. It is 'bi-directional' meaning in the morning it will be one of two lines moving trains into station platforms, and in the evening trains will use it to travel away from the city.

The third line is one of a number of projects currently underway to upgrade Wellington's rail network and give commuters more reliable passenger services. This is a joint initiative between the Greater Wellington Regional Council and KiwiRail.

The Wellington Region Rail Programme includes: A fleet of new electric trains - the Matangi trains Extension of electrification and double tracked lines to take commuter services to Waikanae; Installation of power supply equipment and railway signalling; Adding another line into Wellington Railway Station to reduce delays; Making the Johnsonville Line tunnels larger; and Improving a number of platform and station facilities.