The cost of building a southwest light-rail line from Minneapolis to Eden Prairie would top $1 billion on either of the two favored routes, project officials said Monday.

Ridership on either route would be the same -- 28,000 to 30,000 trips a day -- with about 8,000 of them made by people who would be new converts to transit.

But when comparing cost with travel time savings, just one of the two popular routes -- Route 3A, which passes through Eden Prairie's business district and skirts Cedar Lake in Minneapolis -- is likely to qualify for all-important federal approval and funding.

That points toward selection of Route 3A as the preferred route later this fall.

"We have a project the Federal Transit Administration will find very competitive and want to support,'' said Hennepin County Commissioner Gail Dorfman, who chairs a group of suburban, Minneapolis, county and transit officials who have been studying prospects for the rail line.

Route 3A would run from the new Twins ballpark in downtown Minneapolis to the land corridor between Cedar Lake and Lake of the Isles, and on through St. Louis Park, Hopkins and Minnetonka.

It would end in Eden Prairie, where it would pass through the Golden Triangle business district and past the Eden Prairie Town Center on its way to the final stop at the SouthWest Station.

Uptown route more costly

In terms of political support, Route 3C through Minneapolis' Uptown district is 3A's closest competitor.

Although the two routes have identical 2030 ridership estimates, the forecast range of capital costs for building Route 3A -- $69 million to $78 million a mile -- is far lower than the estimate for Route 3C, $94 million to $106 million a mile.

The 3C Uptown route is more expensive largely because it would require a tunnel to keep train speeds up and trip times competitive with the 3A Cedar Lake route.

Route 3A also has lower operating costs: $23 million to $25 million a year, compared with $27 million to $29 million annually for Route 3C.

And Route 3A promises to save travelers 8,500 to 9,000 hours a year in travel time, 500 to 1,000 hours more than on Route 3C.

The comparisons give 3A a clear edge on the federal cost-effectiveness index, which measures the benefit to travelers vs. the rail line's costs, said Katie Walker, manager of the project for Hennepin County.

She said 3A could deliver the travel time savings that the Federal Transit Administration requires before it allows a project to go on for preliminary engineering

"These are really, really good ridership numbers,'' Walker said. "This is a very strong project.''

The Hiawatha Light Rail has about 30,000 riders a day. Actual ridership has far outpaced the ridership estimates forecast for the line before it opened in 2004.

Lowest cost, but fewer riders

The lowest capital and operating costs for southwest light rail would be realized on Route 1A, which follows a corridor that Hennepin County already owns and uses as the Southwest LRT trail.

Using county land, the cost of building the rail line would be less than $1 billion -- between $850 million to $950 million -- and operating costs would be several million less, between $19 million to $21 million a year.

But the less expensive Route 1A would have lower ridership, because it would not serve Eden Prairie's job centers and business districts. It also lacks political support from Eden Prairie and Minnetonka.

Officials are scheduled to review these figures Aug. 26, and by October recommend a preferred route to Hennepin County. The county is set to finalize the recommendation and forward it for the approval of the Metropolitan Council before the end of the year.

Backers of the southwest line hope to have it open sometime between 2015 and 2017. Construction on the $914 million Central Corridor line, which will run between Minneapolis and St. Paul, is expected to begin late next year, with service starting in 2014.

Laurie Blake • 612-673-1711