ASCE honors HNTB for excellence in highway improvements

News HNTB Corp. March 22, 2006
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HNTB Corp. has been honored by the American Society of Civil Engineers (ASCE), Orange County Branch, for its I-405/ State Route 73 Interchange and Operational Improvements project. The chapter’s “Project of the Year Award” was recently presented at the ASCE Orange County Branch’s Annual Awards Banquet in Costa Mesa, Calif.

The project was also recognized with an “Engineering Project Achievement Award” from the Orange County Engineering Council at its National Engineer’s Week Awards Banquet in Yorba Linda, Calif. Under contract to the Orange County Transportation Authority and in close partnership with the California Department of Transportation’s District 12, HNTB was responsible for final design and construction phase services.

The ASCE award recognizes the accomplishments, quality and diversity of engineering in this vital region of southern California. Design and construction of this complex, freeway-to-freeway interchange project was accomplished in multiple phases beginning in 1997, with construction being completed in early 2005.

Key components of the project included widening of the I-405 freeway to add general-purpose lanes from Bear Street to the Santa Ana River; addition of a new freeway-connector ramp from northbound SR73 to northbound I-405; reconfiguration of the I-405/Fairview Avenue Interchange, including a new flyover-connection ramp from northbound SR73; modifications to the I-405/Harbor Boulevard Interchange including braided, on-and-off-ramps that eliminated operational problems due to short weaving lengths on the freeway mainline. Other improvements included flood control channels, retaining walls, sound walls, landscaping and local street improvements. Major challenges included constructability considerations, coordination among affected utilities, environmental concerns, aesthetics, project permitting and seismic retrofit strategy.

HNTB designed the interchange to minimize the impacts to the adjacent South Coast Drive, Gilser Flood Control Channel and Fairview Avenue Bridge. With the opening of the San Joaquin Hills Toll Road in 1998, this north-end connection to I-405 became an important link in Orange County’s freeway system. One of the biggest challenges was producing a design compatible with future improvements of the Gisler Channel/ Greenville Banning Channel to meet the region’s 100-year flood plain. The Gisler Channel is a major flood-control channel within Orange County.

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