The bridge design satisfied objectives for both architectural and performance. The environmental document required an open structure that would not encroach on the views of the dam or the surrounding terrain of the national historic landmark at Hoover Dam. The engineering performance needed to withstand the demands of wind, earthquake, and service loads well beyond the codified 75-year life.

The approach to design addressed each criterion with a deliberate engineering evaluation and design. The twin arch ribs evolved from the assessment of seismic performance. The arch ribs are reinforced concrete members, designed to be cast with the stayed-cantilever construction method. Cantilever construction of a reinforced concrete box section is rare. This approach was carefully engineered during design on the basis of controlled crack width as well as strength. The elimination of temporary post-tensioning for the arch was a significant savings for construction.

The design team conducted special site studies to address the seismicity of the site and performed an extensive geological reconnaissance as part of a probabilistic site hazards analysis. The resulting design was based on a 1,000-year event, and the PGA was set at approximately double the then codified value. The new AASHTO PGA, established four years after the start of design is approximately the same value as selected for design.

The Hoover Dam Bypass Bridge was built using a variety of limited access techniques in order to gain access from the canyon rims. Excavation was pioneered from the Nevada cliff using mining techniques for limited road access. Two unique 2,500-foot cableways carried workers and 45 tons of material and equipment into place during construction. With cables hanging from 330-foot-tall towers, a 13.5 ton trolley and load block assembly was the key to delivery of men and materials to the work front. The concrete segments for the arches were poured using four headings of self-advancing form travelers. Most of the arch segments were placed at night to avoid the triple-digit desert temperatures reaching as high as 120˚F. Liquid nitrogen was required to control the peak curing temperature of the high performance concrete. Every second arch segment was supported by a temporary stay cable, with tuning required at many stages in order to control geometry. The arch was closed in August of 2009.

Computer models run on site were used by the contractor to calibrate controls used to set headings for the arch cantilevers. This real-time process led to greater construction efficiency, allowing the contractor and designer to communicate in live time with construction, providing for immediate reviews of adjustments to the erection procedures and target geometry. An automatic surveying and monitoring system helped the team to record and analyze how construction operations impacted behavior of the bridge structure, as well as measuring the deflections due to wind and temperature. This data was critical to the arch ribs being properly aligned within ¾ of an inch at closure as the ribs met in the middle of the canyon. A specialized wind monitoring system throughout the project site, including atop the cranes, helped to provide continuous readings to address wind effects on construction operations.

With an average of 14,000 vehicle crossings per day, the stretch of U.S. 93 crossing Hoover Dam impeded the safe flow of traffic along the corridor. The new bridge reroutes traffic from the two-lane bottleneck across the dam, therefore improving driver and pedestrian safety, as well as air quality. Bypassing the dam reduced travel time and fuel consumption for motorists traveling between Las Vegas and Phoenix. Following the 9/11 terrorist attacks, trucks were detoured 23 miles from the dam, costing $30 million annually in delays and fuel consumption along a critical North American Free Trade Agreement (NAFTA) trade route. The Hoover Dam Bypass Bridge benefits the local economy by restoring a critical NAFTA trade route for about 2,000 trucks per day ensuring a safer and faster U.S. 93. America’s newest wonder helps protect the iconic Hoover Dam from possible future threats, while reducing travel congestion for millions of motorists, as well as enhancing the visitor experience for the 3,000 daily tourists visiting the Hoover Dam.