Traffic heading into Wellington between 5am and 7am on weekdays has increased by 50 per cent over the past six years, a new report has found.

Wellington's traffic congestion is getting worse and the morning rush period is becoming longer as commuters try to beat the gridlock.

New figures show traffic heading south into Wellington between 5am and 7am on weekdays has increased 50 per cent over the past six years, with early bird commuters putting further stress on an already under-pressure state highway network.

The result is those trying to beat the rush, which traditionally starts about 6.30am and is at its worst between 7am and 9am, are extending the peak period and making the commutes for those behind them even worse.

KEVIN STENT/STUFF The average speed on SH1, between Wellington Airport and the Basin Reserve, is now 15-20kmh between 8am and 9am.

Unsurprisingly, the increased congestion means travel times for those coming into the CBD from north of the city are becoming less predictable – and they are expected to get even worse.

READ MORE:

* Support for new road at Basin

* City weighs congestion solutions

* Solving congestion no easy task

* Report lays bare transport woes

The findings come from a Greater Wellington Regional Council report that assessed the region's traffic volumes and congestion between 2012 and 2018.

"There is evidence that the peak period congestion is spreading, with people changing their behaviour and travelling earlier to avoid congestion," the report said.

"On the inner city motorway, congestion starts to form around 6.30am with a significant drop in travel speed by 7am, and does not fully dissipate until past 10am."

While the number of vehicles recorded entering Wellington's CBD between 7am and 9am had decreased, that was likely because traffic was moving slower, rather than because of any reduction in congestion.

ROBERT KITCHIN/STUFF Trips in Wellington during peak periods are 34 per cent longer, on average, than they are during free-flow conditions.

If the trend was to carry on, highway congestion would increase even further, more people would travel earlier and congestion problems would start earlier and finish later, the report said.

The growing congestion problem was also apparent on Ruahine St between the Mt Victoria tunnel and Wellington Rd, where two-way traffic prior to 7am increased by 30 per cent between 2011 and 2016.

Those travelling between the CBD and Miramar have also been warned to feel the pinch if Wellington Airport passenger numbers grow as forecast.

KEVIN STENT/STUFF Travel time reliability has decreased on the region's strategic routes.

New Zealand Transport Agency (NZTA) data shows average travel times on six "strategic routes" across the Wellington region increased by 8 per cent in both the morning and afternoon peaks over the past four years – a time period that saw the opening of the $630m Kapiti expressway and Wellington's smart motorway.

The findings come as the Let's Get Wellington Moving project team prepares to release its final proposal for solving traffic congestion between the airport and Ngauranga Gorge in June.

The team is a joint initiative between the regional council, NZTA and Wellington City Council that was born after plans for a Basin Reserve flyover fell over in 2014.

JACK PRICE/STUFF While the number of vehicles entering Wellington's CBD between 7am and 9am has decreased, that is likely due to traffic moving slower, rather than a reduction in congestion.

A shortlist of proposals released in November revealed a number of solutions were being considered, including a fourth southbound lane on the urban motorway between Ngauranga and Aotea Quay, widening Ruahine St, and duplicating the Mt Victoria and Terrace tunnels.

Project director Barry Mein said the findings in the Greater Wellington report were not surprising, and were part of what his team was working to rectify.

"The information in the report is consistent with what we identified earlier in our process," he said.

ROBERT KITCHIN/STUFF Traffic is also building up earlier in both directions on Ruahine St, according to NZTA data.

"There is increased demand for people coming into Wellington and if we don't do anything about it, that's going to continue to be a problem."

WELLINGTON'S TRAFFIC WOES

* 50 per cent more traffic on SH1, from Ngauranga to Aotea Quay, between 5am and 7am

* Average speed on SH1, between Hobson St and the Terrace Tunnel, at 7am is 25kmh

* Average speed on SH1, between Wellington Airport and the Basin Reserve, is 15-20kmh between 8am and 9am

* Amount of traffic using Ruahine St before 7am increased 30 per cent between 2011 and 2016

* Average travel time on the region's six main commuter routes during the morning peak increased from 35 minutes in mid-2014 to 38 minutes in mid-2017.

* Average travel time on those six routes during the evening peak also increased from from 31 minutes to 34 minutes over the same period.

* Travel time reliability has decreased on the region's strategic routes

* Travel during peak periods was 34 per cent longer, on average, than during free-flow conditions in 2016

Source: Greater Wellington Regional Council