California's First Diverging Diamond Interchange

Matt Brogan

Principal + Vice President
Mark Thomas

Matt Brogan has 23 years of experience in transportation engineering. He serves as principal in charge and project manager on a variety of transportation improvement projects starting with planning through final design. His project experience includes local roadway improvements, highway interchanges, corridor studies, bicycle facilities, and civil-related transit improvements.

Aaron Silva has 15 years of experience in design and delivery of transportation projects. Aaron is a proven engineer and geometrician knowledgeable in both local agency and Caltrans design standards. Aaron is recognized as an expert in the design of bike and pedestrian facilities, helping design and implement state of the practice solutions to improve active transportation safety throughout California.

Dave Stanek is a Senior Associate Engineer at Fehr & Peers with more than 24 years of transportation engineering experience. He directs the Multimodal Operations Discipline Group at Fehr & Peers and is a member of TRB’s Highway Capacity and Quality of Service committee. Dave works on complex and challenging transportation problems, serves as a company expert and resource for traffic operations and simulation analysis, teaches training courses on capacity analysis, and develops spreadsheet tools for capacity analysis, model integration, and model output processing.

City of Manteca’s interchange retrofit on Union Road at State Route 120 reconstructed the existing spread diamond interchange to a diverging diamond interchange (DDI). The project was initially conceived to be a full reconstruction to an partial cloverleaf configuration, however the DDI emerged as the preferred design. The DDI utilizes crossover intersections for vehicles to operate on the opposite side of the roadway, which offers many benefits to operations and project costs. Since the first DDI opened in 2009, DDIs are in operation across the country, but none had been implemented in California. The Union Road interchange was the first DDI in the state and and provided unique challenges for design, coordination and implementation.