Bidding for the Southwest light-rail contract has been delayed a third time, meaning construction of the $1.9 billion project won't begin until later this fall.

The new deadline of Aug. 15 was extended "to allow additional time for bidders to prepare bids," said Metro Transit spokeswoman Laura Baenen. Despite the delay, she said passenger service would still begin in 2021.

The news comes at a time when federal funding for big transit projects like Southwest is uncertain.

President Trump's $4.1 trillion fiscal 2018 budget only funds transit lines that have grant agreements in place by October. That's not likely to be the case with Southwest, which is banking on $929 million from the Federal Transit Administration to pay for half the project's cost.

Federal funding is critical to both Southwest and the $1.5 billion Bottineau Blue Line, which would connect downtown Minneapolis to Brooklyn Park.

The 14.5-mile Southwest line, which would connect downtown Minneapolis to Eden Prairie, is complicated — with 29 new bridges, two tunnels for trains and six for pedestrians, more than 100 retaining walls, and modifications to seven existing bridges.

The Metropolitan Council, which is building the line, would not reveal the expected amount of the construction contract, but it is expected to be well over $100 million.

Baenen said the Southwest project office has received more than 670 technical questions from prospective contractors. "The additional time provides potential contractors the opportunity to incorporate responses to those questions in their bids," she said.

The Met Council was heartened to see a $10 million allocation in the temporary $1.1 trillion federal budget approved by Congress earlier this month.

Local funding for Southwest is unclear, as well. On Wednesday, the Counties Transit Improvement Board (CTIB), which is expected to pay 30 percent of the project's cost, will consider a measure to dissolve itself.

The board, which consists of members from five metro counties and the chair of the Met Council, is considering the proposal so that Hennepin and Ramsey counties can increase a transit sales tax to a half cent. They are constrained from doing so as long as the CTIB board exists. A previous move to dissolve the board failed.

Local funding must be shored up before the federal government considers a matching grant.