Last week, the Bottineau Blue Line light-rail extension cleared a meaningful hurdle after elected officials from Hennepin County and the five cities along the line approved the $1.5 billion project's basic route, as well as stations and bridges.

Some believe this 13-mile line, which will link downtown Minneapolis to Brooklyn Park, could be the last LRT project ever built in the Twin Cities. (And still others say: Good riddance.)

But light rail remains among the options for the W. 7th Street corridor between downtown St. Paul and the Minneapolis-St. Paul International Airport and the Mall of America.

Last month, the Riverview Corridor Policy Advisory Committee voted to winnow down possible transit alternatives. In addition to light rail, options include streetcars, both arterial and dedicated bus-rapid transit, and "diesel multiple units," or DMU.

A DMU "is basically a light-rail car that runs on diesel and not electric power," says Kevin Roggenbuck, senior transportation planner for the Ramsey County Regional Railroad Authority (RCRRA).

Common overseas, DMU trains are becoming increasingly used in U.S. cities, including Philadelphia, Portland, Ore., San Diego and Dallas.

The RCRRA is paying $1.9 million to fund the study, which is also probing what route should be used — if any. So far, that's been narrowed down to W. 7th Street and a railroad spur that covers some of the area.

All of the options and routes have pros and cons. Some local businesses fear the loss of parking, should LRT, DMU or dedicated BRT be chosen. (The latter is usually defined as a limited-stop bus that uses a dedicated lane. Arterial BRT simply uses existing streets — the first BRT of this type is the Snelling Avenue line, which begins service on June 11.)

Two years ago, Metro Transit pulled back on the B Line arterial BRT along West 7th, in favor of studying a broader plan that includes the airport and megamall.

The Riverview Corridor itself touches many neighborhoods in St. Paul, including downtown, Lowertown, Upper Landing, West 7th, and Highland Park (including the Ford redevelopment site).

Despite its central location, Roggenbuck says most people agree that current transportation options in the area are lacking.

"People aren't sure if they think we need a future rail or dedicated bus, but by and large people say we need better transit service in that corridor," he said. "The Route 54 bus is really crowded, and the stops are sketchy in places; some people don't like waiting there for the bus."

Other transit officials wonder how the train or buses will cross the Mississippi River, since widening or building a new bridge is an expensive proposition.

For the next two months, the Policy Advisory Committee will be "pairing up modes and routes to see how they work or don't work on these routes," Roggenbuck said. More evaluation and refinement will follow before a series of public meetings in July.

The whole idea is to come up with a "locally preferred alternative," which is transit parlance for the route and mode options that elected officials opt to support. That should come next fall.

But in the scheme of these complicated transit projects, Riverview is still in the very early stages. Even if an alternative is agreed upon by year's end, the project will probably take 10 years to build out.