Enthusiasts of the Midtown Greenway in Minneapolis have long hoped for the popular bike and pedestrian trail to extend into St. Paul on a century-old railroad bridge spanning the Mississippi River. Now, that hope has a new sense of urgency.

A study released by the Midtown Greenway Coalition, a Minneapolis-based nonprofit organization, estimated that refashioning the Short Line Bridge to include a recreational trail would likely cost between $7.4 million and $27.5 million.

“It could be a world-class extension,” said Soren Jensen, the coalition’s executive director, at the study’s unveiling last week.

Paid for by a coalition-led crowdsourcing campaign that raised $46,000, the study presented four options for overhauling the bridge. With this information in hand, coalition members will encourage Hennepin and Ramsey County officials to broach the topic with bridge owner Canadian Pacific Railway.

“We’re hoping the report will kick-start the conversation,” Jensen said.

Canadian Pacific would not permit Kimley Horn, the engineering firm that conducted the study, onto the bridge for the probe. But a drone and photo-imaging techniques helped gather new data.

Canadian Pacific spokesman Andy Cummings said the company “is not in a position to comment, as no formal proposal exists for adding trail access to the Short Line bridge.”

He added that Canadian Pacific “has serious safety concerns with placing recreational trails in proximity to active rail corridors.”

The least-expensive option highlighted in the report suggests shutting down the bridge to rail traffic entirely and converting the span into a bike and pedestrian trail.

Only one train traverses the bridge daily — dropping off and picking up rail cars at the Archer Daniels Midland (ADM) flour mill in Minneapolis, according to the coalition. Recently, ADM announced plans to shutter one of two mills along the Hiawatha Av. corridor, although there’s no indication regarding the fate of the remaining mill.

The second alternative, which would cost about $9.9 million, calls for freight trains and a recreational trail to share the existing span, separated by a 10-foot high metal railing. The third option at $27.5 million suggests partly reconstructing the bridge on its concrete piers, for trains and bikes to share.

And the final option, which would cost about $22.4 million, involves adding an additional deck atop the existing bridge to accommodate the trail. That idea would help stabilize the bridge, which is considered “fracture critical” — meaning if one part of the bridge failed, the structure would collapse.

“It’s an option that could solve some problems,” Cross said last week.

But an official with the Friends of the Mississippi River said the group has reservations about that option because “the scenic and ecological impact could be really damaging,” said Colleen O’Connor Toberman, the group’s river corridor program director. Otherwise, “we’re supportive of using the existing bridge deck or rebuilding it in its current shape and form,” she said.

Talk of extending the Greenway over the rail bridge into St. Paul dates back at least a decade. Hennepin County approached Canadian Pacific about the idea, and the railroad reportedly said the county would have to assume ownership, maintenance and liability for the span, according to Andy Singer, co-chairman of the St. Paul Bicycle Coalition.

In addition, a county-commissioned study by URS Corp. in 2006 recommended against using the existing bridge and estimated that new bike and pedestrian spans on either side of it would cost up to $14 million.

Frequent users of the Greenway aren’t terribly picky about how a connection is made — they’d just like it to happen, as well as an extension of the trail into St. Paul.

“An extension would eliminate a lengthy detour that cyclists and pedestrians currently have to navigate when they are traveling between the Twin Cities,” said Nick Atherton, a graduate student at the University of Minneapolis.

Uptown resident Matt Clark often bikes to work in downtown St. Paul. “There’s no good way to get out of St. Paul on a bike,” he said.

Biking on streets can be stressful, but “once you get over to the Greenway, you can move along,” he said. “It feels very Zen.”