SR-55 Widening

The Project.

Leighton began in Irvine and has operated from here ever since. Our location for the past twenty plus years overlooks the SR 55 / MacArthur interchange, and all the traffic that passes. Currently, an effort between OCTA and Caltrans District 12 would widen the 4-mile segment between the 405 and 5.



  • Geotechnical
  • Environmental

Project Fact:

In 1985, Orange County’s first carpool lane was added to SR-55 between I-405 and SR-91 freeway. Currently, the freeway has a total of five lanes in each direction, including the carpool lane, and provides enhanced traffic flow to more than 300,000 motorists traveling the freeway each day.

The Leighton Solution.

Leighton provided geotechnical and environmental services for the Project Report and Environmental Document (PR/ED). Five alternatives were evaluated involving the addition of auxiliary and/or general purpose lanes in each direction.

Project challenges include its location in a seismically active area and historically high groundwater, which will affect the foundation type selection and associated design parameters, roadway structural sections, and earthwork requirements. In addition, both sides of the corridor are heavily developed, including gas stations, manufacturing facilities, and other commercial and industrial facilities that may have environmentally impacted soils and groundwater. Unpaved areas along SR-55 also may have aerially deposited lead associated with automobile exhaust, meaning soils in the area may require special handling if disturbed during construction.