The TransLink Mayors Council has voted in favour of forging ahead with a plan for a proposed extension of the SkyTrain line from Surrey to Langley, though some of the funding to finish the project remains unclear.

TransLink staff will now proceed with work on the business case for the line, which would run on an elevated guideway for 16.5 kilometres from King George station in Surrey to Langley City along the Fraser Highway.

Surrey Mayor Doug McCallum called the decision a "tremendous win."

"In the end they recognized this project is a big part of our region. It’s one of the fastest growing parts of the region," McCallum said.

"I’m absolutely confident that the line will be completed out to Langley."

The estimated cost for the line is $3.12 billion, if approved and implemented in a single stage.

However, there is only $1.65 billion in secured funding so far, an amount originally intended to go towards the construction of an LRT system covering 27 kilometres, including 104 Avenue and King George Boulevard.

McCallum campaigned on a switch of technologies to SkyTrain, and TransLink was directed to begin looking into the option in late 2018.

The Mayors Council is calling on the provincial and federal governments for more funding to be able to complete the line to Langley as one project, but TransLink staff have also presented options to build in stages, albeit warning the total cost of the project would increase over time.

Currently, the secured funding is enough to extend the line to 166th Street in Fleetwood, estimated to cost $1.63 billion.

That would mean an extension of seven kilometres and four stations.

"We still need to fund it to get all the way to Langley and I would say that’s our biggest challenge ahead of us," said Township of Langley Mayor Jack Froese.

Langley City Mayor Val van den Broek expressed optimism about the project.

"I think 100 per cent we’re going to have it out to Langley. I have no doubt," she said.

As for King George Boulevard and 104th Street, TransLink staff say it would not be possible to provide a full 27-kilometres of rapid transit without surpassing the theoretical funding envelope of $3.55 billion - which they call only a "planning assumption" at this point.

McCallum told the council and media he has no desire to push beyond that notional threshold.

TransLink staff have said only an improved B-line bus service or a partial rapid bus service on those routes could stay keep costs within those boundaries.

The business case for the line will be finalized over the next couple of months, and will include public consultation and environmental reviews.

TransLink says the case would be presented to senior levels of government by January, with possible final approval coming in June 2020.