San Diego Freeway (I-405) Improvement Project

Click here to zoom.

Today, the San Diego Freeway (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 the I-405 are expected to increase significantly and the population is expected to grow 11 percent by 2040.

The California Department of Transportation (Caltrans), in cooperation with the Orange County Transportation Authority (OCTA), is proposing to widen the San Diego Freeway (I-405) between State Route 73 (SR-73) and Interstate 605 (I-605). The purpose of the proposed improvement is to improve travel conditions for work, recreation, school, and commerce by increasing freeway capacity, improving traffic and interchange operations, and enhancing road safety to meet state and federal standards. The I-405 Improvement Project is funded by Measure M Orange County’s half-cent sales tax for transportation improvements.

Project Alternatives

The I-405 Improvement Project draft environmental impact report/impact statement (EIR/EIS) was released on May 18, 2012 and included a no build and three build alternatives. Any project built will include at least one free lane in each direction as part of the I-405 Improvement Project that is funded through Measure M, the county’s half-cent sales tax for transportation.

No-Build Alternative

  • The No-Build alternative leaves the I-405 in its existing configuration with no additional lanes or interchange improvements. 

Alternative 1:  Add one general purpose (GP) lane in each direction

  • Alternative 1, the Measure M2 (M2) Project K as approved by the voters, adds one GP lane in each direction on the I-405 from Euclid Street to the Interstate 605 (I-605) interchange. 

Alternative 2:  Add two GP lanes in each direction

  • Alternative 2 is the M2 Project K with the addition of a second GP lane in the northbound direction from Brookhurst Street to the State Route 22 (SR-22) / 7th Street interchange, and the addition of a second GP lane in the southbound direction from the Seal Beach Boulevard on-ramp to Brookhurst Street. 

On January 26, 2009, the Orange County Transportation Authority (OCTA) Board of Directors (Board) approved the addition of Alternative 3 to significantly alleviate congestion and provide additional travel choices to commuters, as well as to help fund the overall Project during difficult economic times when M2 sales tax forecasts were dropping: 

Alternative 3: Add one GP lane and one high-occupancy toll (HOT)/ express lane in each direction

  • Alternative 3 includes M2 Project K and adds a HOT/express lane in each direction on I-405 from State Route 73 (SR-73) to SR-22. The HOT/express lane would be combined with the existing high-occupancy vehicle (HOV) lanes, and these would be converted to HOT/express lanes providing two HOT/express lanes in each direction on I-405 between SR-73 and I-605. The westbound HOV connector from SR-22 to I-405 would also be operated as a HOT/express lane.

Recent Project Timeline

On October 22, 2012, the Board of Directors selected Alternative 1, Measure M2 Project K, which adds one general purpose lane in each direction.

On April 22, 2013, the Board of Directors directed staff to screen two new concepts for improvements to Interstate 405. Concept A builds the Measure M2 Project K, converts the existing single high-occupancy vehicle lane to a single high-occupancy toll express lane in each direction, and also adds a second general purpose lane in each direction. Concept B builds the Measure M2 Project K and adds a second general purpose lane in each direction, as in Alternative 2, but truncates the second northbound general purpose lane at Valley View Street. For a copy of the April 22, 2013 staff report and presentation, click here.

On June 28, 2013, the Orange County Transportation Authority, in partnership with the California Department of Transportation, released a supplemental draft EIR/EIS which contained additional traffic information, largely in the Long Beach area, not previously contained in the original draft environmental impact report/environmental impact statement. Link to the Supplemental Draft EIR/EIS www.dot.ca.gov/dist12/405/index.htm

Staff presented the findings of the Option A and B Screening as well as a review of public input on the supplemental draft environmental impact report/environmental impact statement at the September 23, 2013 Board of Director’s meeting. For a copy of the staff report and presentation, click here. The OCTA Board did not recommend Concept B for further study.

On September 23, 2013 the OCTA board also voted to continue exploring the addition of toll lanes on the San Diego Freeway (I-405) as a way to improve traffic between Costa Mesa and the San Gabriel River Freeway (I-605) at the L.A. County line.

OCTA is looking at tolling options in carpool lanes in part because last year’s federal transportation bill, known as MAP-21, requires that carpool lanes operate at 45 mph or more 90 percent of the time. Carpool lanes on the I-405 – as well as freeways throughout Orange County and statewide – are failing to meet this standard. Click here for a link to MAP-21. http://www.fhwa.dot.gov/map21/

OCTA Board Action – December 9, 2013

An item regarding the I-405 Improvement Project was recently brought to the OCTA Board of Directors on Friday, November 8 and was subsequently postponed to the December 9, 2013 meeting. Click here for the December 9, 2013 staff report.

On December 9, 2013 the OCTA Board selected Alternative 1 as the Locally Preferred Alternative and recommended that Caltrans select Alternative 1 as the Preferred Alternative in the Final EIR/EIS.

Preferred Alternative Selection 
Caltrans is expected to make a final decision on a project alternative in March 2014.


I-405 Environmental Phase Milestones Chart 

Public Review

May 18 - July 17, 2012

Supplemental Draft EIR/EIS Public Review

June 28 - August 12, 2013

OCTA Board Recommends Alternative 1

Dec. 9, 2013

Caltrans Selects Preferred Alternative

March 2014


July 2014


2015 - 2020


Christina Byrne

Project Contact

Christina Byrne
Manager of Community Outreach
(714) 560-5717