It’s very inspiring to see a growing, grass-roots movement aimed at convincing Minnesota legislators to fund extending the Northstar commuter rail line from Big Lake to St. Cloud.

With that push expected to peak when the Legislature convenes on March 8, backers of the extension need to seriously strengthen their case by addressing very legitimate concerns related to costs and benefits.

On the cost side, most of the public focus has been on the price of extending the line the remaining 42 miles from Big Lake to St. Cloud. St. Cloud Rep. Jim Knoblach has vowed to dig into those costs, which some have projected at about $150 million. Please know, though, that the first section cost $320 million to build.

Still, with the state sitting on a $1.2 billion surplus and pressure mounting to bolster Minnesota’s transportation system with those and other funds, it’s not hard to imagine Northstar in the mix. However, precise estimates for construction are just one cost for which public dollars must be identified.

As proven with the existing rail line, operating costs also pose a serious expense.

A 2012 Minnesota Department of Transportation study about the extension starting in 2017 projected annual rail operating expenses at $3.2 million and its revenue at $464,000, which creates a yearly operating shortfall of $2.74 million. According to the study, which projected such numbers through 2022, that annual shortfall consistently hovers around $2.75 million.

The simple question:  Where will that money come from? And if the idea is to get local or county governments to adopt new taxes or raise existing levies, are they willing to do that? Indeed, Northstar’s history indicates that could be a bigger political challenge than asking a Legislature flush with cash for a piece of that pie.

GRIP/ISAIAH, a faith-based group that pushes for racial and economic equality in Minnesota, is the leading champion of the extension. Its main argument is the benefit for low-income workers, college students, the elderly and communities of color by linking St. Cloud to the Twin Cities and offering a transportation option that doesn’t require a car.

Supporters offer plenty of individuals with examples and anecdotes, plus attendance at grass-roots rallies is impressive. Given the costs involved, though, tangible evidence showing the extension would accomplish those goals is needed.

For example, using Northstar to commute for work — whether traveling to or from St. Cloud — means a 164-mile, 2-hour-plus round-trip train ride likely to cost $10 every workday. (And please note that does not account for the person having to commute from a train station to a workplace.) Are job opportunities and wage rates really that different between St. Cloud and Minneapolis that it will pay for low-wage workers to use the train?

Another point made is how Northstar will help people without cars or the ability to drive. Again, are there studies for similar rail lines nationwide that can supplement anecdotes and examples with ridership statistics or other evidence that shows underserved and struggling populations no longer struggle thanks to rail service?

Supporters, please don’t dismiss such questions as opposition. Rather, provide concrete answers and you will find even more support for this growing movement.