I-405 Improvement Project - History 

I-405 Major Investment Study (MIS) Phase

The I-405 Major Investment Study was an effort by the Orange County Transportation Authority (OCTA) to examine the transportation needs of western Orange County and is part of OCTA's strategic effort to keep Orange County moving over the next 20 years.

Today, I-405 is one of the most congested freeways in Orange County, carrying more than 300,000 vehicle trips in some sections each day. Traffic volumes on I-405 are expected to increase 25 percent with population expected to grow to 13 percent by 2025. This challenge, and what should be done about it, was the subject of the 18-month I-405 Major Investment study.


Click here for study area.

Results of the MIS

Several alternatives for improving travel on the I-405 resulted from an extensive collaboration among the OCTA study team, traffic engineers, local public officials, business and community leaders, and commuters and local residents. These participants gave their time, ideas and comments to the study effort. The alternatives for improvement represent a community consensus about feasible improvements to the I-405 in the years ahead.

In fall 2005, the project’s policy group, consisting of elected officials, city managers and technical staff from each affected city, recommended to the OCTA Board of Directors that only the minimal widening alternative (Alternative 4) be moved forward into the conceptual engineering phase. The OCTA Board ratified this approach by choosing Alternative 4 as the Locally Preferred Strategy in October 2005.

Alternative 4 of the MIS proposes to add capacity in each direction between Brookhurst Street and the San Gabriel Freeway (I-605). It also adds merging lanes, linking an on-ramp to the next off-ramp, in many locations where sufficient right-of-way is available.

I-405 MIS Timeline