SR99-Central Galt Interchange modification, Galt, California, USA

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As part of our integration with Omni-Means, GHD has helped increase interchange capacity for the SR99. Aimed at solving deficiencies and accommodating planned growth within the City of Galt and the South Sacramento County region, the project is aligned with the respective adopted General Plans and the Transportation Concept Report (TCR).

The Central Galt Interchange is the primary access into the downtown area. Recent urban growth, and future growth projected by the General Plan, necessitated a solution to address a currently congested area. We provided 15 alternative design solutions for the selection committee to consider. The resulting design included the reconstruction of all four-interchange ramps, auxiliary lanes on SR 99 to the adjacent interchanges, and two new overcrossing structures.

The approved solution utilizes a split-diamond design to provide access via two main cross-town roadways. The enlarged interchange required the careful mitigation of:

  • Impacts to an existing residential area
  • Channelization of drainage through the area
  • Future linkage to growth areas east of SR 99
  • Impacts to existing vegetation of significant visual quality
  • Relocation of major utilities
  • Buffering existing residential areas and commercial areas

We prepared the Plan, Specification and Estimate (PS&E) and provided construction support, as well as a phased landscape master plan, allowing the City to implement the landscape design as funding becomes available. Our landscape architects also prepared the design of architectural enhancements to the bridge structure.

The project entailed building two closely spaced bridges over SR 99 for adjacent city streets. This required building the A Street Bridge, shifting traffic to it, demolishing the existing C Street Bridge, and construction of the new C Street Bridge.

We worked closely with the City and California Department of Transport to improve the signal timings and coordinate the signal systems to minimize queues. Under this task, ae prepared a synchro model to determine the most appropriate cycle lengths, offsets, and splits for various times of day. Signal timing plans were coordinated and approved by the City and Caltrans.

Road Systems


For more than 50 years, we have delivered innovative road systems including rehabilitation, expansion and development of new highways, complex interchanges, toll roads, bridges and tunnels. Our planners and engineers provide integrated services to plan, design, construct, maintain and manage all aspects of the road corridor life cycle.

From planning and procurement through to feasibility and investigation, and design, construction, delivery and maintenance, our clients enjoy bespoke solutions for roads that incorporate masterplanning, funding and economic analysis, transport planning, asset management, environmental management, risk management and more.

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Transportation Planning & Traffic Engineering


GHD brings a fresh approach to integrated transport with an innovative, dynamic, highly motivated and enthusiastic team of traffic engineers and transport planners who harness a great depth of industry experience and knowledge.

Whether you require high level policy and strategic advice at the beginning of a project or detailed engineering advice at the design stage, you will benefit from the commitment and dedication of our people. We pride ourselves on staying informed of the latest industry thinking and trends through regular involvement in industry bodies, conferences and seminars.

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