The cost of a light rail system for Wellington has skyrocketed to nearly a billion dollars, with Mayor Celia Wade-Brown now conceding it looks unrealistic in the near future.



A detailed business case for light rail between Wellington Railway Station and Kilbirnie was made public for the first time today.



It put the cost of building the network at $940 million, largely because it would require its own tunnel through Mt Victoria.



Light rail was one of three options being looked at as part of the Wellington Public Transport Spine Study, which is aimed at finding the best solution to the capital's public transport needs for the next 20 to 30 years.



The study was a joint initiative between Wellington City Council, Greater Wellington Regional Council and the NZ Transport Agency, who will be splitting the cost of the chosen option.



After about 18 months of research, independent consultants AECOM found light rail would cost almost five times more than the next most expensive option - a bus rapid transit system (better bus lanes and bigger buses) for $207 million.



The third and cheapest option was a bus priority system (better bus lanes) for $59 million.



Ms Wade-Brown, who was elected three years ago on the back of campaign promises to push for light rail in Wellington by 2020, was singing a different tune today.



"While light rail is attractive, bus rapid transit may be a more immediate and pragmatic step and I want significant progress well before 2021," she said.



"Let's build a better public transport system now, starting with more bus priority lanes in 2014."



A bus rapid transit system through central Wellington was found to have the most benefits of three possible options, followed by light rail and then a bus priority system.



The Wellington Regional Transport Committee, which has representatives of all the region's councils and the transport agency, will receive the report tomorrow and decide the next steps, leading to a decision on a preferred option. Public consultation is likely next year.



Jenny Chetwynd, the transport agency's central region director, said the preferred option would have to be affordable for ratepayers, public transport users and road users.



''At this point it seems that the [bus rapid transit] option provides the best balance between transport benefits and value for money."



Greater Wellington chairwoman Fran Wilde said the study provided a ''springboard'' for an informed debate about future public transport.



BUS PRIORITY ($59 million)

More peak bus lanes and priority traffic signals for buses along the Golden Mile and Kent and Cambridge terraces, around the Basin Reserve, along Adelaide Rd to Newtown and through the Hataitai bus tunnel to Kilbirnie.

3.2 per cent increase in the number of people using public transport region-wide during the morning peak.

$35 million* in time savings for public transport users.

$88 million to run annually.

Planning could begin in the next few years, with the network being developed incrementally as opportunities arise.

BUS RAPID TRANSIT ($207 million)

A dedicated busway for higher-capacity buses, such as articulated or double-decker buses, along the Golden Mile and Kent/Cambridge Terrace, around the Basin Reserve, along Adelaide Rd to Newtown and through the duplicated Mt Victoria tunnel to Kilbirnie.

Almost halves the travel time between Kilbirnie and Wellington Railway Station.

7 per cent increase in the number of people using public transport region-wide during the morning peak.

$95 million* in time savings for public transport users.

$83 million to run annually.

Planning would begin in 2021-22 with the network being built all at once.

LIGHT RAIL ($940 million)

New tram vehicles running on dedicated tracks along the Golden Mile, Kent and Cambridge terraces, around the Basin Reserve, along Adelaide Rd to Newtown and through a dedicated Mt Victoria tunnel to Kilbirnie.

Almost halves the travel time between Kilbirnie and Wellington Railway Station.

No change in the number of people using public transport region-wide during the morning peak due to the need to transfer between light rail and bus services for travel beyond Newtown and Kilbirnie.

$56 million* in time savings for public transport users.

$89 million to run annually.

Planning would begin in 2021-22 with the network being built all at once.

Contact Michael Forbes

Transport and metro reporter

Email: michael.forbes@dompost.co.nz

Twitter: @michael_forbes