Engineering Excellence & Legacy Awards

The Fourth Street Bridge project removed a longstanding traffic bottleneck by reconstructing and providing wider twin bridges over Interstate 40 (I-40) in Flagstaff, Arizona. Initially built in 1968, the bridges remained in a two-lane configuration as adjacent sections of Fourth Street were widened to four and five lanes, creating a traffic bottleneck and congestion during peak travel times. The project also added pedestrian walkways connecting to the Flagstaff Urban Trail System and dedicated bicycle lanes on the bridges to enhance safety, particularly for students traveling to and from elementary and middle schools on either side of I-40.

“Providing connections that improve people’s lives” is the core purpose of the Maricopa County Department of Transportation (MCDOT). To accomplish this, MCDOT developed the Transportation System Plan (TSP) 2040 to guide the planning of limited resources for a large geographic area. The TSP 2040 establishes a plan for the future transportation needs of Maricopa County residents across three planning horizons – 2025, 2030, and 2040 – after a thorough review of the MCDOT transportation system, planning documents and processes, stakeholder plans, and funding information.

The TSP 2040 reaffirms the goals, objectives, and strategies from MCDOT’s previous TSP 2035, strengthens them with guiding principles and performance measures for current and future transportation needs and investments, and complements Maricopa County’s Comprehensive Plan guidelines for transportation. The TSP 2040 comprehensively addresses transportation system needs beyond capacity, including active transportation, safety, Intelligent Transportation Systems (ITS), drainage, structures, pavement preservation, and PM-10 (air quality). Identifying these needs and the opportunity for holistic improvements continue to drive MCDOT’s core purpose of improving the system for all users.

The Prescott Regional Airport (PRC) New Terminal project had quite a few site constraints and complex civil elements, which required unique and innovative thinking from Dibble. This included varying grade differentials, complex phasing, a constrained project site, and creating a new signature entrance to the airport from the redesigned State Route 89. All of these complexities were challenged by the existing terminal, adjacent hangars, and airport administration building, and all airport operations had to remain open and functional throughout this project.

One of the main goals of this project was to replace the deteriorating asphalt pavement with an appropriate pavement structural section that could support the sustained heavy truck loading this roadway generates, while reducing long-term maintenance issues. During the preliminary design phase, the project team worked together to perform a life-cycle cost analysis of various surface pavement, base course, and subgrade types. This analysis compared the relative pavement strength, upfront construction costs, reoccurring maintenance costs, and design life/replacement costs over 50 years. The types of material and construction techniques analyzed included surface courses of asphalt pavement, traditional Portland Cement Concrete Pavement (PCCP), fiber-reinforced PCCP, and a special proprietary “Opti-Pave” concrete installation technique; base courses including aggregate base, recycled asphalt, and cement-treated base; and subgrade reinforcement such as cement or lime-treated subgrade and geogrid or fiber mesh.

The City of Avondale (City) continues to be one of the fastest-growing communities in the West Valley. Recognizing the need to plan for additional resources to support this growth and improve the water system’s reliability and redundancy, the City began to explore ideas to supplement the City’s water portfolio. It engaged Carollo to prepare the City’s 2018 Integrated Utility Master Plan (IUMP). As a result of the IUMP, the northern portion of the City was identified to benefit from an additional water supply supporting growth and providing operational flexibility in Zones 1 and 2. The North Avondale Water Supply Project (Project) implements one of the major solutions to bring a new potable water source conceived during these planning efforts.

The Val Vista Water Treatment Plant (VVWTP) Rehabilitation Project 2018 included a comprehensive condition assessment, design, and construction. The condition assessment was used as part of the prioritization process to identify the necessary rehabilitation or upgrades for key assets and treatment processes at the plant. VVWTP is jointly owned by the Cities of Phoenix and Mesa and is operated and maintained by the City of Phoenix. Carollo Engineers performed the assessment, design, and engineering services during construction, and Sundt Construction served as the Construction Manager-at-Risk (CMAR), providing preconstruction and construction services.

With world-class winter sports and pristine outdoors attracting visitors from around the world to the state, Colorado enjoys a vibrant aviation system serving the state’s thriving economy that includes significant business activities, including aviation and aerospace. The 66 public-use airports in the system operate independently, striving to serve the state’s aviation demand, both from commercial and general aviation users. To evaluate the needs of the statewide system, not just summarize individual airport-identified needs, the Colorado Department of Transportation Division of Aeronautics (Division) has historically undertaken the Colorado Aviation System Plan (CASP) and separate economic impact analysis. Both have been updated utilizing the same baseline and framework established over 20 years ago.

Typically, tiebacks are angled at 20 degrees from horizontal. However, the drill rig boom could not fit into the tight excavation space and still drill into the vertical shoring wall surface at that angle. The site required avoiding the light rail subsurface right-of-way and reaching the higher soil friction material 23 feet below the surface as efficiently as possible. The design team installed the tiebacks at 45 degrees from horizontal to solve these issues. This method allowed the tiebacks the quickest, safest, and most constructible route into the high-friction native sand-gravel-cobble material.

The project connected the City of Goodyear to its Central Arizona Project (CAP) surface water allocation through the Salt River Project (SRP) canal system. The pipeline and water treatment facility brought Goodyear surface water for the first time, providing the city and surrounding communities with a secure, resilient, and renewable water future.

Typically, tiebacks are angled at 20 degrees from horizontal. However, the drill rig boom could not fit into the tight excavation space and still drill into the vertical shoring wall surface at that angle. The site required avoiding the light rail subsurface right-of-way and reaching the higher soil friction material 23 feet below the surface as efficiently as possible. The design team installed the tiebacks at 45 degrees from horizontal to solve these issues. This method allowed the tiebacks the quickest, safest, and most constructible route into the high-friction native sand-gravel-cobble material.

With world-class winter sports and pristine outdoors attracting visitors from around the world to the state, Colorado enjoys a vibrant aviation system serving the state’s thriving economy that includes significant business activities, including aviation and aerospace. The 66 public-use airports in the system operate independently, striving to serve the state’s aviation demand, both from commercial and general aviation users. To evaluate the needs of the statewide system, not just summarize individual airport-identified needs, the Colorado Department of Transportation Division of Aeronautics (Division) has historically undertaken the Colorado Aviation System Plan (CASP) and separate economic impact analysis. Both have been updated utilizing the same baseline and framework established over 20 years ago.

The Mesa Drive project was much more than a roadway project. It included every major element of a public works project, from utility pipelines to structures to electrical distribution conversion to traffic signals and intelligent transportation systems (ITS). This multi-discipline nature required a diverse team of 8 sub-consultants during design and 35 trades to construct. It improved the undeveloped section between the two legacy projects described previously.

The project added a new water treatment train- the plant’s fourth to expand treatment capacity by 15 million gallons per day (MGD). A critical project criterium was to keep a passive flow, split to the existing three trains and the new one. This was a challenge because of the fourth train’s location relative to the headworks. Also, the design needed to account for future treatment expansion.

The Fourth Street Bridge project removed a longstanding traffic bottleneck by reconstructing and providing wider twin bridges over Interstate 40 (I-40) in Flagstaff, Arizona. Initially built in 1968, the bridges remained in a two-lane configuration as adjacent sections of Fourth Street were widened to four and five lanes, creating a traffic bottleneck and congestion during peak travel times. The project also added pedestrian walkways connecting to the Flagstaff Urban Trail System and dedicated bicycle lanes on the bridges to enhance safety, particularly for students traveling to and from elementary and middle schools on either side of I-40.

Typically, tiebacks are angled at 20 degrees from horizontal. However, the drill rig boom could not fit into the tight excavation space and still drill into the vertical shoring wall surface at that angle. The site required avoiding the light rail subsurface right-of-way and reaching the higher soil friction material 23 feet below the surface as efficiently as possible. The design team installed the tiebacks at 45 degrees from horizontal to solve these issues. This method allowed the tiebacks the quickest, safest, and most constructible route into the high-friction native sand-gravel-cobble material.

The Prescott Regional Airport (PRC) New Terminal project had quite a few site constraints and complex civil elements, which required unique and innovative thinking from Dibble. This included varying grade differentials, complex phasing, a constrained project site, and creating a new signature entrance to the airport from the redesigned State Route 89. All of these complexities were challenged by the existing terminal, adjacent hangars, and airport administration building, and all airport operations had to remain open and functional throughout this project.