I-405 Improvement Project

405 Project Logo

OCTA in cooperation with Caltrans is widening the San Diego Freeway (I-405) between SR-73 and I-605.The project will improve 16 miles of I-405 between the SR-73 freeway in Costa Mesa and I-605 near the L.A. County line.

The project includes adding one regular lane in each direction between Euclid Street and I-605 and making improvements to freeway entrances, exits and bridges. In addition, the project will add the 405 Express Lanes, incorporating the existing carpool lanes and a new lane in each direction between SR-73 and I-605.

For more information, please contact the Outreach team by calling 888-400-8994 or visit their website.

Project updates surrounding the City of Los Alamitos:


August 22, 2023 Construction Alert: Southbound (SB) and northbound (NB) I-405 will close nightly in Seal Beach and Westminster to install traffic detectors and an overhead sign.

SB I-405 will close nightly between Seal Beach Boulevard and eastbound (EB) SR-22 as early as 11 p.m. to 5 a.m.

Closure Dates: Tuesday, Aug. 22; Wednesday, Aug. 23; and Thursday, Aug. 24.

NB I-405 will close nightly between Seal Beach Boulevard and westbound (WB) SR-22 as early as 11 p.m. to 5 a.m. 

Closure Dates: Wednesday, Aug. 23; and 11 p.m. to 6 a.m. Friday, Aug. 25.


SB I-405 will also close between Bolsa Chica Road/Valley View Street and Springdale Street 

Closure Dates: Friday, Aug. 25 at 11 p.m. through Saturday, Aug. 26 at 6 a.m.







NB I-405 will also close between Valley View/Bolsa Chica and SR-22 

Closure Dates: Thursday, Aug. 24 at 11 p.m. to Friday, Aug. 25 at 5 a.m.







SB Seal Beach On-Ramp REVISEDFebruary 1, 2022 Construction Alert: Crews will close the southbound (SB) I-405 on-ramp from Seal Beach Boulevard for approximately one month to accommodate the freeway widening.

The ramp is scheduled to close 10 p.m. Wednesday, Feb . 2, and is anticipated to reopen after approximately one month.






July 1, 202West Seal Beach Boulevard Sidewalk1 Construction Alert: Crews closed the sidewalks at the intersection of Seal Beach Boulevard and Lampson Avenue for permanent traffic signal construction.
Activities include the removal of existing sidewalk ramps, installation of new sidewalk ramps, electrical and foundation work.

Permanent traffic signal construction began Tuesday, June 1, and will continue for approximately two more months, on weekdays.  

Daytime work hours are 9 a.m. to 3 p.m. 

Seal Beach Boulevard and Lampson will be intermittently reduced to two lanes at the intersection for the duration of the work.
• Nighttime temporary traffic signal removal and permanent pole installation are anticipated in early July.



Freeway Closures Detours for Bolsa Chica 1Freeway Closures Detours for Bolsa Chica 2








June 10, 2021 Construction Alert: Crews will continue to perform girder installation work for the Bolsa Chica Road bridge over I-405. The girders are the main horizontal support beams and are part of the superstructure.

This work will require SB and NB full freeway, lane, SB Bolsa Chica Road, and ramp closures.

Night One

• SB freeway closure is set for as early as 11 p.m. TONIGHT, June 10, to 5 a.m. Friday, June 11.   

• SB Bolsa Chica and SB loop on-ramp closures are set for 10 p.m. TONIGHT, June 10, to 5 a.m. Friday, June 11.  

Night Two

• NB freeway closure is set for as early as 11 p.m. Friday, June 11, to 5 a.m. Saturday, June 12.   

• SB Bolsa Chica closure is set for 10 p.m. Friday, June 11, to 5 a.m. Saturday, June 12.  


Bolsa Chica Road Bridge Work Part 2Bolsa Chica Road Bridge Work









June 3, 2021 Construction Alert: Crews will install pre-cast concrete girders for the Bolsa Chica Road bridge over I-405. The girders are the main horizontal support beams, known as the superstructure, the abutments and center columns.

This work will require SB and NB full freeway, lane and ramp closures.

Night One

• SB freeway closure is set for as early as 10:30 p.m. Friday, June 4, to 7:30 a.m. Saturday, June 5   

Night Two

• NB freeway closure is set for as early as 11 p.m. Saturday, June 5, to 8 a.m. Sunday, June 6   

*If this activity has not been completed, during the timeframes above, work is anticipated to continue on Monday, June 7 from 11 p.m. to 5:30 a.m.


WB SR 22 On0Ramp

April 9, 2021 Construction Alert: Crews are set to close the Old Ranch Parkway on-ramp to the WB SR-22 for approximately eight months to realign it as part of the I-405 Improvement Project. Activities include demolition, excavation, grading, drainage and electrical system installation, concrete pours and asphalt paving.

Beginning as early as 10 p.m. Tuesday, April 13, for approximately eight months. 

• Daytime work hours are 7 a.m. to 4 p.m. 

• Crews may mobilize equipment as early as 6 a.m.

• Nighttime work hours are 9 p.m. to 6 a.m.

Motorists should expect delays and use alternate routes if possible. All closures and detours will be included in our interactive map (https://i405improvements.kleinfelder.com/), on our closure list and on the project website. 

Please be advised that this work may be loud. Dates and times are subject to change due to unforeseen operational factors or inclement weather.


Construction Alert

April 8, 2021 Construction Alert: Partial Lane Closures on Seal Beach Boulevard for Median Work. Crews will install temporary traffic signals at Seal Beach Blvd. and Lampson Ave. and at Seal Beach Blvd. and the northbound (NB) I-405 freeway ramps/Old Ranch Parkway.

Temporary traffic signal construction is anticipated to start as early as 10 p.m. Friday, April 9 for approximately two weeks on weeknights. 

Seal Beach Blvd. and Lampson Ave. will be intermittently reduced to two lanes at the intersection for the duration of the work. Nighttime work hours are 9 p.m. to 6 a.m.




Seal Beach Blvd Median Construction
March 26, 2021 Construction Alert:Crews will begin median removal activities on Seal Beach Boulevard between Lampson Avenue and Old Ranch Parkway. This work will require continuous lane reductions on Seal Beach Blvd. for the duration of the work.

The center median will be demolished, removed and reconstructed to allow for the addition of a second left-turn lane from southbound (SB) Seal Beach Blvd. to the northbound (NB) I-405 on-ramp.

Activities include median removal, landscaping/tree removal, excavation, concrete work, backfilling, striping and street/median restoration.

Median work is anticipated to begin as early as 10 p.m. Monday, March 29, and continue for approximately one week on weekdays. 

• Daytime work hours are 7 a.m. to 4 p.m. Crews may mobilize equipment as early as 6 a.m.

• Nighttime work hours are 9 p.m. to 6 a.m.

Motorists should expect delays and use alternate routes if possible. All closures and detours are included in our interactive map (https://i405improvements.kleinfelder.com/), on our closure list and on the project website.

Please be advised that this work may be loud. Dates and times are subject to change due to unforeseen operational factors or inclement weather.


I-405 Improvement Project_Seal Beach to 22 Connector_Final2October 15, 2020 Construction Alert: Full southbound (SB) I-405 closure between Seal Beach Boulevard and SR-22 SB is set for 11 p.m. Saturday, October 17, to 7 a.m. Sunday, October 18.

I-405 Detour is:

SB I-405 off-ramp to Seal Beach → SB Seal Beach → Eastbound (EB) Westminster Boulevard → SB I-405 on-ramp

EB SR-22 Detour is:

EB SR-22 off-ramp to Seal Beach → SB Seal Beach → EB Westminster → Northbound (NB) Bolsa Chica Road → EB Garden Grove Boulevard→ EB SR-22 on-ramp


NB Seal Beach

June 27, 2020 Construction Alert: Crews are closing the northbound (NB) I-405 on-ramp from Seal Beach Boulevard during the day to continue pile driving activities for a wall adjacent to the ramp.
The daytime closure is set for 6 a.m. to 1 p.m. Thursday, June 18.
The detour is:
• NB Seal Beach Boulevard → NB Los Alamitos Boulevard → Westbound (WB) Katella Avenue →Southbound (SB) I-605 on-ramp → NB I-405







JuBolsa Chica Road Bridge Demone 15, 2020 Construction Alert: Crews will begin median removal activities on Seal Beach Boulevard between Lampson Avenue and Old Ranch Parkway. This work will require continuous lane reductions on Seal Beach Blvd. for the duration of the work.

The center median will be demolished, removed and reconstructed to allow for the addition of a second left-turn lane from southbound (SB) Seal Beach Blvd. to the northbound (NB) I-405 on-ramp.

Activities include median removal, landscaping/tree removal, excavation, concrete work, backfilling, striping and street/median restoration.

Median work is anticipated to begin as early as 10 p.m. Monday, March 29, and continue for approximately one week on weekdays. 

• Daytime work hours are 7 a.m. to 4 p.m. Crews may mobilize equipment as early as 6 a.m.

• Nighttime work hours are 9 p.m. to 6 a.m.

Motorists should expect delays and use alternate routes if possible. All closures and detours are included in our interactive map (https://i405improvements.kleinfelder.com/), on our closure list and on the project website.

Please be advised that this work may be loud. Dates and times are subject to change due to unforeseen operational factors or inclement weather.


May 26, 2020 Construction Alert: Crews will begin pile driving activities to100323869_2976455445768844_3278406519095296000_n build the foundation of the Magnolia bridge. Approximately 130 piles will be used.

The activity will occur along northbound and southbound I-405 and in the freeway median at Magnolia. 

Some activity, such as equipment mobilization and hauling materials, may occur at night. 

Beginning as early as Tuesday, May 26, 2020. Daytime schedule 7 a.m. to 4 p.m. and nighttime schedule 10 p.m. to 5 a.m. This activity is anticipated to last approximately one month.

Please be advised that this work may be loud. Dates and times are subject to change due to unforeseen operational factors or inclement weather.



CA - NB I-405
May 5, 2020 Construction Alert: Contractors on behalf of the Orange County Transportation Authority (OCTA) will be conducting drainage work as part of the I-405 Improvement Project. Daytime closures are set for Tuesday, May 5th through Friday, May 8th between 6 a.m. and 4 p.m.