By: David Meier, P.E. Contributing Author
More than 105,000 vehicles enter the intersection of 114th Street and West Dodge Road each day, making it the busiest intersection in Omaha, Neb. With traffic on West Dodge projected to top 157,000 vehicles per day (vpd) by 2025, a five-year construction undertaking totaling $102 million will improve a 1.8-mile segment of West Dodge and eliminate the gap in an existing freeway. A new overpass at 114th will be in place by the end of 2007.
Nebraska Department of Roads (NDOR) commissioned the project, which includes dual 40-ft-high, 1-mile-long expressway bridges carrying three lanes of traffic both eastbound and westbound. Nearly 70% of West Dodge traffic currently traveling through the 114th Street intersection is anticipated to use the expressway lanes. Local traffic will continue traveling on the existing at-grade West Dodge Road.
Success in the final design phase of the West Dodge Expressway meant preparing well-coordinated plans that accommodated a significant structural change, addressed a number of unique elements and provided a comprehensive construction phasing plan.
Elevating the game
As the project moved into final design, the elevated expressway was expanded from an original plan of two lanes in each direction to three lanes in each direction. This was prompted by a 20,000-vpd increase in traffic projections resulting from the Metropolitan Area Planning Agency (MAPA), extending traffic projections from a design year of 2020 to 2025 and, more significantly, increasing the level of anticipated development in and near the West Dodge corridor.
Although the elevated roadway could be widened to include the extra lane, the narrow footprint available for expressway bridge piers between West Dodge and its parallel frontage roads had not changed. Cantilevers for the hammerhead piers increased, and the narrow columns were subjected to added loads. Fortunately, some expandability had been included in the proposed two-lane expressway section, so widening could be held to 6 ft and limit increased column loads. The left shoulder was narrowed except for areas where super elevation sloped toward it, in which case a 6-ft shoulder was maintained. A crown was added between the right-hand driving lane and shoulder to limit the amount of pavement draining to areas with the 6-ft shoulder.
Detailed description
Without a doubt, detailing the construction phasing and traffic control plan was the toughest task of the final design. With traffic volumes of 60,000 to 80,000 vpd along the project and millions of square feet of development accessing West Dodge via cross roads and frontage road driveways, plans for the expressway had to include keeping traffic moving throughout construction.
Use of a movable barrier system to provide a reversible lane on West Dodge was considered but ultimately rejected because three lanes were needed in each direction during morning and afternoon peak periods. Access to adjacent businesses along the parallel frontage roads was another strict requirement, but in most cases access was temporarily limited to a single driveway.
Bridge construction over much of the existing roadway lanes on West Dodge and frontage roads complicated phasing and traffic control. The solution was a phasing plan in which critical portions of the expressway bridges were built one at a time and frontage roads rebuilt in short segments, allowing traffic to be shifted out from under the bridges. Off-peak lane closures and overnight directional closures on West Dodge permitted construction of pier foundations and caps, girder erection and deck pours. A schedule for closures and lane-rental provisions was defined in the special provisions.
The city of Omaha and NDOR reached an agreement during final design that all at-grade West Dodge lanes would be reconstructed, a prerequisite for city assumption of maintenance responsibility. The added reconstruction caused the overall construction schedule to be extended by a season to allow West Dodge work to be done after the expressway lanes were open, when a majority of the traffic would be using the elevated expressway lanes. Despite the reduced traffic volume, maintenance of traffic during the final phase was complex, since a total rebuild of the 114th and West Dodge intersection was included.
Since the project was to be let as three packages with largely concurrent schedules, it was necessary to coordinate traffic maintenance from package to package and with an overlapping project to reconstruct the adjacent interchange of West Dodge Road with I-680. The maintenance of traffic plans and special provisions were structured to limit traffic-control responsibilities to no more than two contractors at any time during the combined duration of the West Dodge projects.
Including hardscaping
Adjacent property owners and businesses were concerned the elevated expressway bridges would look overbearing and detract from property values. The bridges also would have an extensive footprint in which grass and shrubs would not survive. It was evident that hardscape treatments had to be identified for the under-bridge areas.
In response to public and stakeholder input, an urban architect was added to the project team early in final design to infuse ideas for enhancing the appearance of the structures. With final design already under way, decisions on aesthetic features to implement were needed quickly, and the creative development of ideas had to be closely coordinated with the design team. One of the features added—a change in the shape of the bridge piers from rectangular to octagonal-shaped columns—triggered structural design revisions, although the shape proved to be very efficient regarding placement of reinforcing within the pier section.
Adding graded berms and low terrace walls under the bridges and around piers to create visual interest spurred extensive interaction between the landscape architect and bridge and roadway engineers. The challenge was to negotiate the extent of special grading, since pier foundations were largely designed by that time. Hardscape design for areas under the bridges involved a combination of concrete pavers, grouted stone and textured, colored pavement to provide variety in color and texture while limiting the amount of required maintenance. The final plans also incorporated a three-tone colored coating scheme applied to piers, selected girder surfaces and barriers as well as texturing and color treatment of retaining walls to simulate natural limestone blocks. Decorative lighting along the outer faces of the expressway bridges and floodlights to illuminate the piers were other elements of the aesthetic features. A landscaping package was prepared for at-grade medians and areas where existing right-of-way allows room for trees, shrubs and native grass. Aesthetic features account for approximately 7-10% of the total estimated construction cost.
Winter plumbing
Public concerns for ice and snow removal on the expressway bridges combined with consideration of their length and a 6% grade on a portion of the bridges prompted investigation of technology available to mitigate winter conditions. Research on available systems yielded that chemical spray systems are the most proven option currently in use. Technical proposals and cost estimates for the system and installation were obtained from the three primary U.S. suppliers, followed by individual presentations. Anti-icing system owners from a range of locations, including Colorado, Michigan, North Carolina and Pennsylvania, were contacted for input on system performance and supplier track record.
All of the information gathered was built into an evaluation matrix that included supplier experience, system components and effectiveness, strengths and potential weaknesses, reference checks and cost. With an emphasis on buying the most advanced technology for detection and prediction of icing conditions, automated activation and a strong performance record, a preferred supplier was identified. The supplier was selected prior to construction letting, with FHWA concurrence, so the anti-icing system design could be closely coordinated with bridge design.
Design required integrating what essentially is a large plumbing system with the bridge decks, girder arrangement and pier design. Since the detailing by the anti-icing supplier did not start until bridge design was nearly finished, and because NDOR wanted anti-icing system components to be accessible for maintenance, the system was detailed using more of a retrofit approach instead of embedding the pressure piping within the bridge decks. The biggest challenges were developing details for the pressure piping to accommodate expansion movements of the bridge and coordinating pressure piping runs to avoid crossing over or through bridge girders.
Pump house locations and configurations were worked out with the landscaping design to limit visibility and achieve aesthetic compatibility. NDOR opted to expand the anti-icing system to include smaller bridges on the east end of the project and connecting roadways; so two systems ultimately were designed, with installation split over two construction packages.
A post-letting decision has been made to install only elements of the system embedded in piers, bridge decks and under slabs, with other system components deferred to a later date.
The team works
The final design phase on the West Dodge Expressway reinforced the need to closely coordinate between bridge, roadway, traffic and other design team members and foster a strong sense of teamwork. Regular team meetings and cross-checking between disciplines are critical to avoid or minimize problems, errors and omissions. Decisions on special features, such as aesthetic treatments, are best made prior to the final design phase, and the creative development should be coordinated with designers to minimize impacts and avoid unfeasible ideas. Pre-selection of a specialty item like an anti-icing system greatly improves its coordination with other elements of the project and should minimize construction phase problems.
Construction of the West Dodge project began in 2003 and currently is tracking ahead of schedule. The expressway overpass will be finished in late 2007; reconstruction of West Dodge at-grade from east of 120th Street to east of 114th Street will occur during 2008, with completion probably by late fall.
About The Author: Meier is senior project manager for HDR Inc., Omaha, Neb.
