The Drive: Why rebuild Cedar and Portland bridges simultaneously, readers ask?

It's to the mailbag we go this week, and the burning question on the minds of many Drive readers is: Why in the world did Hennepin County decide to bulldoze the bridges on Portland and Cedar avenues that span the Midtown Greenway at the same time?

The county closed both south Minneapolis thoroughfares between 28th and Lake streets on May 8, and that has transformed the normally smooth commutes for the 25,000 motorists who cross the bridges each day into dashboard-pounding drives.

For the past two weeks, motorists have been caught in jams on congestion-clogged Chicago Avenue and sought refuge on other nearby streets such as Bloomington Avenue as they navigate around the closures, which will be with us until the two new $4 million bridges open in December.

"We've heard from people feeling the traffic," said county spokesman Kyle Mianulli. "I don't blame them for feeling frustrated."

Mianulli said there are several reasons the county decided to tackle both projects concurrently, rather than replacing one bridge this construction season and the other next year.

First, the county wanted to be sure both routes are open before the Minnesota Department of Transportation gets to work on a $240 million rebuild of I-35W between Lake Street and I-94 scheduled for next summer. That project includes extending MnPass lanes between 46th and 26th streets, building a transit station in the center of I-35W at Lake Street, adding exits on southbound I-35W at Lake Street and northbound I-35W at 28th Street, and rehabbing pavement and bridges. Many freeway lanes and the ramp from northbound I-35W to westbound I-94 will be shut down. Talk about a major traffic disrupter.

With all that chaos looming in 2018, Mianulli said it was imperative that Cedar and Portland get done this year.

Reason 2: Replacing the century-old bridges in a single season provides efficiencies for contractor C.S. McCrossan. The bridge builder can coordinate materials and use innovative techniques, including doing some prefabricated work: The contractor can assemble sections of the bridges off site, then bring them in and slide them into place. That approach was used last year when the county rebuilt the Franklin Avenue bridge, and it sped up the process.

Reason 3: The county can stage closures along the Midtown Greenway and keep it open for trail users while the bridges are being built.

The bridge rebuilds have been on the county's calendar for a couple of years, but it took time to muster resources and coordinate plans with the city and historical preservation organizations, Mianulli said. "The plan all along was to do them at the same time," he said. The idea is "to reduce the long-term impact to the area."

When completed, the new Cedar Avenue bridge will have three 13-foot-wide lanes and a 3-foot buffer to separate traffic from a bike lane. Portland will have two 11-foot-wide lanes and one 13-foot lane. In the meantime, Mianulli says the county will work with the city of Minneapolis to improve signage to better direct drivers.

"We do watch traffic closely," Mianulli said. "We are in an adjustment phase as people are still adapting their travel routines. We don't expect that to continue through the construction season."

Follow news about traffic and commuting at The Drive on startribune.com. Got traffic or transportation questions, or story ideas? E-mail drive@startribune.com, tweet @stribdrive or call Tim Harlow at 612-673-7768.