Capital commuters' favourite game of "guess when your train is going to arrive" will soon be over.

From the middle of this month, real time passenger information displays will go live across the Wellington region, beginning with the Johnsonville line before expanding region-wide by the end of September.

The system uses satellites to track the precise position of trains in order to predict their "real" arrival time at each station.

People at platforms will not be the only ones who benefit. The GPS information will be available online, via text message, and through the Metlink call centre.

When the calibration was correct, arrival times were accurate to within 30 seconds, Greater Wellington regional councillor Peter Glensor said.

"Some years ago it became clear in our conversations with the community that this was the top priority for commuters - that knowing when their train or bus would arrive was the single biggest thing."

The same technology was rolled out on Metlink buses between 2011 and 2012.

All up, the project has cost Greater Wellington and the NZ Transport Agency $8.4 million, which includes the cost of 250 information displays and tracking devices for 464 buses and 74 trains.

Mr Glensor said the bus data had proven accurate. On the few occasions it was not, the issue was normally human error, such as a driver forgetting to switch on the GPS tracker before starting a route.

"We're being very careful to ensure that when this system goes live, it'll be working properly. Because there's nothing worse than a new system like this not working and people losing confidence in it."

The real-time data might highlight timetable areas that could be tightened in order to improve train services, he said.

Lyndon Hammond, the Transport Agency's regional manager of planning and investment, said real-time information would make services more user-friendly and contribute towards easing congestion.