A rendering of a train along the planned Southwest Light Rail line, passing through the Kenilworth Lagoon in Minneapolis. The line is to run between Minneapolis and Eden Prairie. (The Minnesota Star Tribune)

Finally — and in the nick of time — it's a sure thing: The extension of the Green Line best known as Southwest Light Rail will be built, on a timetable that calls for service to commence in 2023.

That welcome news came Wednesday in the form of a "letter of no prejudice" from the Federal Transit Administration (FTA), which is expected to pay roughly half the cost of the $2 billion public works project, the largest in state history. It arrived just one day before the expiration of the sole remaining construction bid, $799 million from Lunda/C.S. McCrossan.

With that letter in hand, the Metropolitan Council and Hennepin County's rail authority can initiate construction spending on the 14.5-mile project with confidence that an essential federal match for local spending will follow, likely next spring. While the letter makes no promise, no major transit project in the country has ever been denied federal funding after advancing to this stage in the approval process.

The timing of Wednesday's letter was not a coincidence, said Hennepin County Commissioner Peter McLaughlin, the de facto captain of the team of Minnesota civic and business leaders who have championed this project during nearly two decades.

Many Minnesotans, including Gov. Mark Dayton during his hospital stay in Rochester, were in personal contact with FTA leaders in recent weeks to convey the message that the loss of the one remaining bid would deal the Southwest project a major blow. Further delay after several bid extensions already seemed likely to result in cost increases that would unravel the complex deal.

That would have been a major setback to this region's development aspirations. Southwest represents the next phase of a plan developed and executed by several generations of the Metropolitan Council — under both Republican and DFL governors — to give this region a mass-transit network worthy of the major population center it has become.

Four lines — two light rail, two bus rapid transit (BRT) — are already in operation. Initial construction has begun on the Orange BRT line. Southwest is the sixth leg of a staged system build-out whose next steps include Bottineau light rail to the northwest and the Gold BRT line in the east metro.

Delaying Southwest likely would have set back those projects as well — at a time when demand for rapid-transit services is growing. Ridership on both the Green and Blue lines is well ahead of forecasts; both set ridership records in 2017 and are on track to do so again in 2018.

Along the tortured path Southwest light rail has taken to reach this point, it faced stiff resistance from a variety of quarters. Opposition to transit from the GOP-allied fossil fuel industry and skepticism in greater Minnesota about its cost contributed to the partisan obstacles it faced at the Legislature in 2015-16.

McLaughlin and the Hennepin County Board then took ownership of the project, raising a transit-dedicated 0.5 percent sales tax in 2017 to keep it alive. He worked in close concert with Metropolitan Council chair Alene Tchourumoff and the heads of the state and regional business organizations, who lent a lobbying hand with the FTA.

McLaughlin's leadership was on many minds when the FTA's go-ahead letter was received. He lost a bid for an eighth term in the Nov. 6 election to political newcomer Angela Conley, a candidate who complimented his transit leadership but argued for more diversity on the board.

"This secures Peter's legacy," said Tchourumoff, who will also soon leave her post for a position with the Minneapolis Federal Reserve Bank. We concur. But we also hope McLaughlin's public service is not over.

Gov.-elect Tim Walz and the Legislature ought to have a transportation funding boost high on their to-do list for 2019, and McLaughlin would be an asset in getting it done.