Hamilton Construction and Oregon DOT 'Thread the Needle' at Fern Valley Interchange
With the final permanent ramp now open on Oregon's first "diverging diamond" design interchange at exit 24 of the I-5, a major project reaches one of its final milestones to completion. The interchange is in the city of Phoenix, Oregon, about 24 miles north of the Oregon and California border.
The $72 million Fern Valley Interchange project, which began construction in February 2015, has a scheduled end date in September. Hamilton Construction, of Springfield, Oregon, is the general contractor.
Oregon Department of Transportation (ODOT) Public Information Officer Gary Leaming said the project is on track to finish on time, save for some landscaping that needs to occur in cooler weather.
Multiple Moving Parts
The project is complex, involving the I-5, Oregon 99, North Phoenix Road and Fern Valley Road, with new bridges over the I-5 and at Bear Creek, about a half-mile west of the I-5 on Fern Valley Road to connect with Highway 99. Several existing local streets were reconstructed, the realignment and reconstruction of a local road and the construction of a new local street. The project also includes work related to the City of Phoenix waterline relocations and reconstruction.
A major consideration in the design and implementation of the project is the proximity of homes and businesses to the highway.
Leaming said, "The biggest challenge was keeping everyone connected and businesses accessible during the construction process." With the available space restricted by existing roads and shopping areas, the final footprint of the project needed to be narrow, and in phasing the construction, he said, "We were threading a needle."
Temporary ramps were in use throughout much of the construction and traffic went under the existing bridge to a signal that routed traffic via a local road to the 99 and the shopping mall.
To help ensure work zone safety, ODOT implemented a number of measures including TripCheck traffic cameras, the Rogue Valley's Incident Response vehicle, transverse rumble strips and a reduced speed limit to 50 mph.
The Oregon State Police patrols the work zone. Traffic fines double in work zones, even when there are no workers present. TripCheck cameras were installed to help keep an eye on traffic in the work zone.
Interchange Addresses Long-Standing Needs
Leaming noted that the existing interchange dated back to the 1960s and had become inadequate to the needs of the burgeoning population of Phoenix and the Rogue Valley. The interchange experienced traffic congestion throughout the day, and particularly during the morning and evening commutes. Existing and proposed development along the east side of I-5, as well as development growth within the Rogue Valley, challenged the capacity of the interchange and created safety concerns.
Work on design for the project began in 2004. By 2009, authorities sorted through siting options and approved an Interchange Area Management Plan specifying that the new interchange will accommodate projected traffic volume growth through at least 2030. They also secured funding, which included a $25 million investment from the 2009 Oregon Jobs and Transportation Act. Much of that funding is based on increases in truck weight-mile flat fees, registration fees, road use assessment fees, and heavy vehicle trip permit fees.
The ODOT project team collaborated with a consortium of private contractors to develop construction methods for the project, taking into account challenges including the close proximity of the new bridge ramps to the existing ramps.
Choosing Diverging Diamond
In a first for Oregon, and the West Coast of the U.S., the new Fern Valley Interchange features a Diverging Diamond interchange design.
This is a variation of the standard diamond interchange commonly used where a freeway crosses a minor road. As in the standard diamond interchange, the freeway and other road are grade-separated. With the Diverging Diamond, the difference is that the two directions of traffic on the road cross to the opposite side on both sides of the bridge at the freeway. So traffic in that section is driving on the opposite side of the road.
The diverging diamond interchange allows for two-phase operation at all signalized intersections within the interchange. This also improves safety, as drivers don't have to make any long turns have to clear opposing traffic.
The Diverging Diamond design was a good choice for Phoenix, said Leaming. The goal was to reduce the project footprint and reduce the project's impact on surrounding businesses, as well as the right of way costs. The design also provides better traffic capacity and safety for motorists.
The Missouri Department of Transportation was the first in the United States to construct an interchange with this diamond design, on Interstate 44 at the intersection with Missouri Highway 13 in Springfield. In 2010 The ODOT project team traveled to Missouri to study the new design first hand. They found that the new design moves traffic efficiently and safely through a previously congested intersection in a major commercial area.
To help motorists see how to use the diverging diamond interchange, ODOT produced a 3-D traffic simulation video to illustrate how the new interchange design would work. The video is still posted on the project website, though drivers have been using the diverging diamond system since February.
Remaining work on the project includes final paving on the west side of the interchange, new traffic signals and the opening of the Bear Creek Bridge.
With the new interchange almost complete, local officials and residents are focusing on future benefits of the project.
Phoenix Mayor Jeff Ballah wrote in an ODOT publication,"Retail, light industrial and other developers will want to build near the high-capacity interchange. Approximately 400 acres near there will be brought into our urban growth boundary with part of it providing some relief for much-needed residential development."
Ballah added, "The project will help provide a jump start for our urban renewal efforts in our city center on the west side of I-5. Along with our move to single-lane traffic on Highway 99, the new traffic patterns from this project help meet our plans for a small business- and pedestrian-friendly city center."