The proposed Blue Line light-rail extension cleared an important milestone this week after Crystal and Robbinsdale joined three other cities and Hennepin County in approving the project’s basic route and infrastructure, including stations and bridges.

Also known as Bottineau LRT, the $1.5 billion project would connect Brooklyn Park with downtown Minneapolis — and points beyond on the existing Blue and Green lines, such as Union Depot, the University of Minnesota, the Minneapolis-St. Paul International Airport and Mall of America. The line is scheduled to begin passenger service in 2021.

State law requires that cities grant “municipal consent” of preliminary plans for the 13-mile route, which also snakes through Golden Valley.

After a discussion that lasted more than 90 minutes on Monday, the Crystal City Council opted to take “no action” on its Bottineau resolution, which is still a type of approval. The vote was 4-2.

Crystal was the first city to levy such a decision since the state adopted the municipal consent law, according to Dan Soler, Blue Line extension project director.

Because only 15 percent of the project’s design has been completed so far, some Crystal officials groused that it’s difficult to approve plans they see as preliminary, and before final environmental studies are completed.

“This process is ridiculous,” Council Member Elizabeth Dahl said at Monday’s meeting. “Even if you vote no, it has no teeth. … It’s not respectful of our city or our citizens.”

Robbinsdale unanimously gave consent on Wednesday, but outlined 17 “items of concern” in its resolution.

And, earlier in the process, residents from the Harrison neighborhood on Minneapolis’ North Side said they were worried about protracted construction, possible gentrification of the working-class area and safety along Olson Hwy.

Soler said Blue Line staff considers “comments from each of cities on the plans, the resolutions and feedback. We take in all that stuff.”

But other municipal officials and residents expressed support of a project that will not only link the northern suburbs to the downtowns of St. Paul and Minneapolis, but to the southwestern suburbs, which will be served by the planned Southwest light-rail line.

“This is a very big week for Bottineau, it’s a great victory,” said Hennepin County Commissioner Mike Opat, who represents several cities along the line. “I have never seen this kind of excitement for a project, especially one on the North Side where there hasn’t been a lot of investment.”

By late August, Blue Line staff will have 30 percent of the design plans completed and apply with the Federal Transit Administration (FTA) to begin the project’s engineering phase. Heavy construction is slated to begin in 2018, lasting about two years.

The FTA is expected to pay 49 percent of the project; the Counties Transit Improvement Board 31 percent, and Hennepin County and the state each contributing 10 percent.