Project NEON is one of the biggest and most expensive public works projects ever built in Nevada. The new bridge was a sorely needed addition to the state’s highway infrastructure to accommodate rising rates of traffic. Before the project, the area of highway outside of Las Vegas was already seeing frequent traffic jams and an average of four accidents every day—and traffic in this area is expected to double by 2035.
The massive project involved creating a connector bridge between Interstate 15 and U.S. Route 95 by widening and reconstructing 3.7 miles of the interstate. It resulted in the first high-occupancy vehicle (HOV)–dedicated interchange in southern Nevada and has had a dramatic impact on traffic in the area.
The designers initially considered a steel-plate girder design, but they ultimately chose a California wide flange girder to achieve the most efficient structure possible. “We chose the California girders after comparing them to several other girder shapes,” said Allan Mills, project manager with Kiewit. “From the technical side, these girders allow for increased reinforcing in the bottom flange and increased stability. The use of these girders in combination with high-performance concrete and wider girder spacing allowed the design team to utilize fewer girders and achieve longer spans.”
Savings covers cost of another bridge
Once the team established the superstructure design basis, they selected a five-girder layout with 13 ft 9 in. spacing and 3 ft 6 in. overhangs. It was an ideal choice for a steel-plate girder design, but it had never been done with precast concrete girders. After all feasible efficiency modifications were evaluated, calculations supported the proposed spacing. Following more analysis and optimization, designers landed on a girder spacing of 13 ft 7.5 in. Engineering students at California State University, Sacramento, confirmed the spacing feasibility and sensitivity.
With variable deck overhangs, the span lengths around the radius of the bridge were limited to just 150 ft. Greater span lengths within the curve would have created too little or too much overhang, which would have required transverse post-tensioning. Precast concrete girders constructed with self-consolidating concrete proved to be well suited for this span.
The design efficiencies realized by using precast concrete on the bridge resulted in such significant savings that enough money was leftover to add an additional bridge replacement to the project.
Thanks to this new bridge, travel delays will likely be reduced by 28%, which will yield $110 million in annual savings through increased productivity.