Work is set to begin next spring on the rebuilding of the Hwy. 169/Interstate 494 interchange to relieve one of the biggest bottlenecks for commuters from the southwest metro area.

To the cheers of the 75,000 drivers who take Hwy. 169 daily, the project will remove the last three sets of stoplights on Hwy. 169, upgrading the segment of the west suburban road through Bloomington, Eden Prairie and Edina from a stop-and-go expressway to a freeway.

C.S. McCrossan and Edward Kraemer and Sons, a joint venture, appear to have won the contract to design and build the interchange at a cost of about $125 million.

The contract will be awarded in mid-November and the work must be finished no later than August 2013, said Michael Beer, Minnesota Department of Transportation project manager.

The design of the project will stand out in two ways.

In a departure from national design standards, the interchange will have just six of the eight freeway-to-freeway ramps federal policy requires on such major interchanges. MnDOT's agreement with the Federal Highway Administration will require MnDOT to build two more fly-over ramps later if traffic problems develop on nearby roads in Edina and Eden Prairie. MnDOT will monitor traffic patterns at four locations for indications that traffic levels warrant construction of the extra ramps.

Another unusual feature of the interchange design will be a constellation of six roundabouts for local traffic on the frontage roads and local roads surrounding the interchange.

"Normally the local access is provided at a local interchange some distance away from the freeway-to-freeway interchange," Beer said. On I-494 at Interstate 35W, for example, access is at Penn and Lyndale Avenues and 76th and 82nd Streets, he said.

At the 169-494 interchange, serving local traffic will require six intersections spaced relatively close together on the roads ringing the freeway, Beer said. Based on projected traffic demand, "these six intersections could have been a mix of signals, four-way stop signs and two-way stop signs.

"Using six roundabouts in close proximity to each other will allow traffic to flow more freely, greatly reducing the possibility that traffic could back up from one intersection into another intersection," Beer said.  "It also provides for a uniform intersection control method for each of these six intersections. "

To save money, the segment of four-lane Hwy. 169 opened in 1997 through Bloomington and Eden Prairie with stoplights instead of freeway overpasses at three intersections. The cost of the entire stretch from I-494 to Hwy. 101 was $30 million.

But the lights caused safety problems and delays from the outset. Construction of overpasses removed signals at the Pioneer Trail and Bloomington Ferry Road/Anderson Lakes Parkway crossings in 2004 and 2006. Those overpasses cost about $20 million to add.

That left delays at the remaining lights at Highwood Drive, south of 494, and on either side of the bridges over 494. MnDOT had a chance to remove them in 1999 when bridges over 494 were deficient and had to be replaced. But there was no money to build a signal-free interchange, so the department fixed the bridges and left the lights.

It took most of the past decade for MnDOT to line up funding for the new interchange. And it required winning permission of the Federal Highway Administration to build a less expensive freeway design.

MnDOT argued that it would save $30 million by leaving out fly-over ramps from east 494 to north 169 and from south 169 to west 494. Traffic forecasts show that relatively few vehicles would use those ramps because most motorists in that area travel in those directions more conveniently by using the nearby Hwy. 212.

Initially the highway administration insisted that any interchange design must conform to national requirements.

But ultimately, the administration agreed to the more modest project on the condition that MnDOT would build the two additional fly-over ramps later if they are needed.

Starting in October of the year the interchange is finished, MnDOT will look annually at:

Whether congestion is worsening in the nearby interchange at Crosstown Hwy. 62 and Hwy. 169;

Whether it takes more time to drive between Eden Prairie and Edina on Hwy. 212 than on I-494.

Whether it's taking drivers significantly longer to drive W. 78th St. and Washington Avenue between Eden Prairie Mall and Braemar Park in Edina.

And whether the number of midday crashes in the area is increasing, which would be an indication that motorists are confused or frustrated.

MnDOT will make annual reports on each location to federal highway officials. The understanding between the two agencies is that construction of the two missing ramps will be required if traffic reaches problem levels at two of those four locations -- unless MnDOT builds other road improvements that reduce the congestion at those locations.

Laurie Blake • 612-673-1711