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Reconstructing the Highway 169 and Interstate 494 Interchange

Thu July 05, 2012 - Midwest Edition

Reconstructing the cloverleaf interchange at Trunk Highway 169 and Interstate 494 in southwest Minneapolis to a flyover system will convert Trunk Highway 169 into a freeway from an expressway to improve safety and mobility.

The project area includes Trunk Highway 169 between Valley View Road and Anderson Lakes Parkway, and I-494 between Prairie Center Drive and West Bush Lake Road.

The intersection provides access to local suburbs of Edina, Bloomington and Eden Prairie and is a major corridor to the popular vacation area north of the Minneapolis/St. Paul Twin Cities area. Traffic congestion at the interchange, especially on Trunk Highway 169, was caused partially because the previous configuration had three traffic lights with increasing traffic numbers.

“The previous intersection included loops and once you were on Trunk Highway 169 had you had to stop at the signals,” said John Griffith, west area manager with the Minnesota Department of Transportation’s metro division. “So removing the signals and adding free flow is addressing a lot of those problems.”

In the mid-1990s, the Minnesota Department of Transportation replaced bridges on Trunk Highway 169 spanning I-494, reconfiguring that interchange. Work at that time helped improve safety but it was not intended to be a final resolution. Projected traffic growth indicated there would still be congestion until a more comprehensive project could be done. The existing Trunk Highway 169 bridges will be used in this current project, Mn/DOT information explains.

Leading up to this current project, morning and evening rush hour traffic would back up to Trunk Highway 62 and sometimes to the north to Anderson Lake Parkway, about 1 mi. away, Griffith said.

Average daily traffic on Trunk Highway 169 is about 133,000 vehicles each day, according to information from the Minnesota Department of Transportation, while average daily traffic numbers on I-494 are about 136,000. Interstate 494 is the southern portion of a beltline that circles the Twin Cities, extending more than 100 mi. (161 km)

This $125.3 million project began in 2011 and is expected to be completed by November 2012. Work includes reconstructing the interchange with six connections, removing traffic signals, connecting the north and south frontage roads under Highway 169, building noise walls and constructing drainage and water quality facilities. About $16 million in utility and communication relocations created some challenges as finalizations were awaited in order for work to proceed. About 49,126 linear ft., roughly 9.3 mi. (14.5 km) of sewer pipe will be placed. Six retention ponds also are being constructed throughout the intersection.

Through discussions and negotiations with the Federal Highway Administration (FHWA), the design and construction of this project proceeded with a performance based design, which is based on the performance and needs of a specific area, according to information from the Minnesota Department of Transportation. The performance based design rebuilds the interchange with six ramps instead of eight as a phased approach instead of constructing all eight at once, which is the current federal policy for interstate highways. It removes stoplights, reduces congestion and improves safety, thus meeting 90 percent of the areas needs while saving costs.

Four flyover bridges are also included in the new configuration to ensure continued traffic movement. Auxiliary acceleration and deceleration lanes will be added in each direction on Trunk Highway 169 through the interchange, allowing motorists more time to exit or access the highway, helping to keep traffic flowing in order to change this portion of the highway into a freeway.

In 2011 crews under the joint venture of C.S. McCrossin Inc., of Minneapolis, Minn., and Kraemer & Sons of Plain, Wis., and 31 subcontractors managed to stay on track, even with some major setbacks. Northbound Trunk Highway 169 was reconstructed as was the new Washington Avenue Bridge spanning I-494. This new bridge will make it easier for local residents to access their neighborhoods. The new Washington Avenue Bridge is expected to take some of the pressure off of the Valley View Road interchange, which is just north of this new Highway 169 interchange, that is quite congested due to the close proximity of ramps, frontage roads and signals, said Michael Beer, design build project manager with the Minnesota Department of Transportation’s Edina office.

The flyover bridge from westbound I-494 to southbound Trunk Highway169 also was partially constructed in 2011, while the frontage road system was partially reconstructed. Two roundabouts were opened and Trunk Highway 169 traffic signals were disabled.

Early in the 2011 construction season, setbacks occurred due to spring flooding and an unforeseen government shutdown.

“For the most part the project is going well, but spring flooding that caused several crossings over the Minnesota River west of the project to be closed, forcing additional traffic onto the Trunk Highway 169 overpass, and the government shutdown in July last year caused some delays,” Beer said. “With the increased traffic during the flooding, the contractor converted all the signal systems to right hand, right out only. That was a bit of a challenge but it worked well to maintain traffic flow through 2011 into 2012.”

In an effort to catch up, changes to traffic sequencing were made and some grading and paving work was moved from 2011 to 2012 to keep traffic safe. The project should still be completed on time, Beer said.

Griffith added that work was extended into the milder-than-average winter season, to help make up some of the lost time.

“Originally, the contractor planned on rebuilding southbound Highway 169 and northbound Trunk Highway 169 in 2011 but with the state shutdown, it would have pushed construction of southbound Trunk Highway 169 into winter,” Beer said. “For the safety of the traveling public, the contractor decided not to start work on southbound Trunk Highway 169 until spring. Otherwise, we would have traffic pinched head-to-head on four narrow lanes and we didn’t want to do that during the snow season.”

The construction site also contains mucky soils that have to be dealt with. In most cases, where it was practical, the mucky soil was replaced, Beer said. But in some places the poor soil extended roughly 10-ft. (3 m) down and so couldn’t be replaced. Instead, geo piers were used to create support. The predicted settlement under some of the footings for the retaining wall foundations was determined to exceed contract requirements so geo piers were used to increase the native soil stiffness under these spread footings, Beer said.

Geo piers require aggregate and vibration for compaction. The aggregate compacts vertically and horizontally to fill any voids around the column of aggregate, according to technical reports. The installation is quick, there is less vibration and it is cost effective, Beer added. Mn/DOT also is measuring the stress of the steel pipe piling to determine its structural capacity as it is driven into the ground. This also increases efficiency.

Workers are now into the second year of construction and tackling a huge portion of the project. Crews are reconstructing southbound Trunk Highway169, finishing the remaining work on frontage roads, which includes Washington Avenue, Viking Drive, West 78th Street and Marth Road, and opening the remaining four roundabouts. They also will finish constructing the flyover bridges, ramps and loops.

The area is congested with numerous pieces of equipment on any given day, including cranes such as a 35-ton American 4250, two 50-ton American 5299 crane, a 100-ton Link-belt LS338, a 45-ton American 4260 crane, a 150-ton American 9270 crawler, and a 100-ton Manitowoc 10K crawler — to lift the 2,600 tons (2,359 t) of structural steel into place.

Other equipment includes two Delmag D19-42 Diesel pile hammers, a Delmag D25-32 diesel pile hammer, numerous blade rippers, backhoes, pavers and dozers from D5s to D8s to assist with the grading and placement of 102,000 linear ft. (31,090 m) of concrete curb and gutter, and 54,396 tons (49,347 t) of rebar. Backhoes will assist with the removal of 1,292,400 cu. yds. (988,111 cu m) of common excavation.

According to information from Mn/DOT, the signal at Highwood Drive was removed and Highwood Drive will no longer connect to Trunk Highway 169. Marth Road on the south side of I-494 and West 78th Street on the north side of I-494 will have new access under Trunk Highway 169. The Washington Avenue extension to Marth Road will provide a new north/south connection over I-494.

Griffith added that when realigning these roadways they tried to stay within the existing alignment as much as possible but two of the frontage roads had to be reconstructed with new horizontal and vertical alignments. “The new alignment of Trunk Highway 169 is basically the same as where it was. We tried to stay with the existing foot print as much as we could. Work on I-494 is not affecting the alignment,” Griffith said.

Of the four flyover bridges, of which one was shortened so the curve is shorter than is typically thought of for a flyover bridge, and one bridge was moved, Beer explained. Of the other three bridges, as of early June, one deck was poured and the concrete barrier was to be poured shortly thereafter. On another bridge the steel was set and plywood was being placed to pour the deck. On the final bridge the curved steel girders were ready to be placed. The lengths of the remaining three flyover bridges vary including 1,092 ft. (333 m), 510 ft. (155 m), 121 ft. (37 m) and 966 ft. (294 m)

Six roundabouts are also included in the project at West 78th Street, Washington Avenue and Marth Road. These additions as a whole create a new circulator road, allowing traffic to drive around the Highway 169/Interstate 494 interchange from Washington Avenue to West Bush Lake Road, information from Mn/DOT explains. Roundabouts are not commonly seen in Minnesota but are being constructed at some intersections that have a high crash rate or where more than two roads intersect in an effort to reduce accidents.

Statistics show that roundabouts show a 39 percent decrease in all crashes and an 89 percent decrease in fatal crashes. They also can handle high levels of traffic with less delay than most stop signs or signals. The tight curves of the roundabouts slow traffic so entering and exiting is easier and more efficient.

Two roundabouts at Washington Avenue are complete, while work continues on the remaining four. Roundabouts can be created in less space than a typical four-way intersection, but traffic control is a bigger issue, Griffith said. In this situation the anticipated traffic growth was considered and stopping time at a four-way intersection and it was determined that roundabouts would be the best alternative.

“Because of the newness of the roundabouts people are not used to driving through them so they don’t immediately realize it is not a stop condition but a yield condition,” he added. “Once they are used to driving through them they are pretty efficient.”

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