It looks like Calgary city council may have to pull the emergency brake on the Green Line tunnel through the downtown core.

An administration report going to Wednesday’s Transportation and Transit committee meeting outlines how the tunnel may be too risky because of cost uncertainty, especially during harsh economic times.

“Obviously, having trains go underground is more ideal,” said Ward 6 Coun. Jeff Davison on Tuesday.

“Unfortunately, we have different geology here that makes it much more challenging. At a time when council is looking to have cost assurances on mega projects, going underground might not be the best option for us today.”

Council had previously approved the plan to tunnel from 16 Avenue N. in Crescent Heights, continuing under the Bow River and through much of the downtown until resurfacing in the Beltline neighbourhood near 12 Avenue S.E.

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But with new reports waving a red flag over cost uncertainty, the mayor said there is still time to make the right decision.

“This is a good time in terms of construction. Prices are still low, so it’s a great time to go forward and build major infrastructure. But you got to do so in a way where you want to be on time and on budget — my favourite four words,” said Mayor Naheed Nenshi.

“If there is an enormous risk that you are going to go over budget by building a tunnel, then that is a discussion we have to have.” Tweet This

Construction on Stage 1 of the project is set to begin next year.

It would cover 20 kilometres of the proposed line from 16 Avenue N. to 124 Avenue S.E. in the community of Shepard. It would also use all of the $4.65 billion previously approved for the Green Line. It’s unknown where the rest of the money would come from.

WATCH: City of Calgary video shows what the Green Line LRT could look like based on the March 2017 design.

Ward 9 Coun. Gian-Carlo Carra was asked if reconsidering the tunnel or considering a cheaper version might save the city a bundle, reduce the risk and possibly extend the first stage of construction to include more stations.

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“The headline is yes; it’s both of those things,” said Carra. “We are trying to maximize the bang for the buck we have and to execute the line in a way that allows us to deliver everything we want to deliver and potentially more.”

Council will review its options behind closed doors at Wednesday’s meeting, and then go public with its decision.

Nenshi said he is confident any changes made will not delay the first stage of the project. The next big deadline is to have a shortlist of potential contractors by July.