After years of study, the Metropolitan Council faced two imperfect options for the Southwest light-rail line: Reroute a freight-rail line through St. Louis Park, or run light-rail trains through two nearly half-mile-long shallow tunnels on either side of the channel connecting Cedar Lake and Lake of the Isles in Minneapolis.

Despite opposition that still poses a threat to the project, the Met Council was right to choose the shallow-tunnel option for the Kenilworth corridor, pending formal approval as early as this week.

To be sure, the designated options were the flawed product of an unwieldy process. Many in Minneapolis — including Mayor R.T. Rybak, several candidates to succeed him and several members of the City Council — are deeply disappointed that the Met Council did not recommend moving the freight-rail line.

But for the transit project, as well as for the city of Minneapolis, the shallow tunnels have advantages over running light-rail trains at grade.

Construction will be a disruptive hassle. Once that's complete, however, the impact of the nearly 220 weekday light-rail trains will be greatly mitigated. Instead of being entirely visible, the trains will surface only for about 20 seconds as they move from tunnels north and south of the channel.

The few daily freight trains will remain at grade. And, importantly, the existing Kenilworth hike and biking trails, which are critical commuting connections, will be retained at grade.

The shallow-tunnel option does not require that any homes or businesses be acquired. The freight-rail reroute option through St. Louis Park would have required taking 32 properties in that community. And much of the rerouted freight line would have needed to be built on 22-foot high berms through residential neighborhoods and business districts, near the high-school football field and even through an elementary school playground. St. Louis Park residents, citizens groups and elected officials were justified in resisting this option.

The St. Louis Park option also would have been more expensive, costing an estimated $200 million, compared with $160 million for the alternative. The shallow-tunnel plan also saves several Minneapolis townhouses that would need to be acquired if light rail were at grade in the narrowest portion of the corridor.

There are legitimate environmental concerns, and the limited space between two lakes heightens the risks. Rybak rightly focused on the potential impact of the shallow-tunnel option when he said at last week's Corridor Management Committee meeting that, "I don't believe we have put to bed the question of what impact this could have on the Chain of Lakes."

If the shallow-tunnel plan is adopted, it will be imperative that the Met Council ensure that the lakes — justifiably considered by many to be the city's natural crown jewels — not be damaged during construction or operation. For now, the Met Council is citing a technical review commissioned by the Minnehaha Creek Watershed District, which concluded that there was low risk of flooding or groundwater impact.

The fact that the district's opinion was both preliminary and qualified is worth noting, though. "Not expected" and "reasonable way to minimize" aren't good enough. There can be no margin of error on this issue.

Minneapolis — as well as St. Louis Park, Hopkins, Minnetonka and Eden Prairie — soon will be asked to give municipal consent to the Met Council's plan. Assuming the vote occurs before the Nov. 5 election, current Minneapolis officials, many of whom are among the region's most ardent transit advocates, will be asked to support the project for the greater good of the Twin Cities. Some will rightly cite previous promises not to colocate the freight-rail line in Minneapolis. They'll also continue to call for an independent freight-rail analysis after a consultant selected by the Met Council withdrew because of a conflict of interest. Federal funding that would cover half the cost of the $1.55 billion project is at stake, however, so it's time to move forward.

Just as tough decisions had to be made with the Hiawatha and Central Corridor light-rail lines, Met Council officials faced difficult choices. They made the right call. Minneapolis officials should do the same, or risk derailing the much-needed transit line for good.