State Route 120 / Guthmiller Road Interchange Improvement

Project Description

The City of Lathrop, in cooperation with Caltrans, the San Joaquin Council of Government (SJCOG), and the Federal Highway Administration (FHWA) proposes to improve local and regional circulation and reduce existing and future congestion by improving the I-5 /Louise Avenue Interchange.  The project is locally sponsored.  Interchange improvements are needed to enhance traffic operations and mobility which will accommodate future traffic demands as a result of the growth planned in the City of Lathrop’s General Plan.

The I-5 / Louise Avenue interchange is a Type L-1 tight diamond configuration, with single lane on and off-ramps.  Recent improvements have provided for turning movements by widening at the ramp termini.  River Islands Parkway has been improved and widened to provide access to the Mossdale Landing, River Islands, and Central Lathrop developments.

The reconstruction of the interchange (Alternative 2) may close Manthey Road at River Island Parkway.  The remaining properties will be accessed from Golden Valley Parkway.  Golden Valley Parkway is a major arterial that parallels I-5 and replaces Manthey Road within this area.

The project proposes to replace the existing tight-diamond (L-1) I-5 / Louise Avenue Interchange with one of the following two (2) project alternatives:

  • Alternative 1 – Diverging Diamond Interchange (DDI)
  • Alternative 2 (from PSR) – L-1 (east side) / L-9 (west side) Partial Cloverleaf-Tight Diamond Interchange (PC-TD)


Project Benefits


The purpose of the project is to improve the existing SR 120/Yosemite Ave interchange to accommodate existing and planned traffic in Lathrop. More specifically, the purpose of this project is to:

  • Improve local access to SR 120
  • Improve regional mobility on SR 120
  • Relieve congestion on SR 120, and local roadways during peak hour conditions.


The project is needed because traffic generated by planned and approved developments is anticipated to exceed the existing operational capacity of the interchange. The interchange is currently a compact diamond design and is anticipated to degrade to level of service (LOS) "F" (i.e., forced or breakdown flow) under existing plus project conditions.


Funding Source

Crow Holdings Industrial, Local, Federal.


Project Cost/Programmed

Projected Cost as of (June 18, 2019) Planned $
Project Approval & Environmental Document $6,350,000
Plans, Specifications, & Estimates $2,320,000
Right of Way $3,620,000 - $14,260,000
Construction $25,000,000 - $37,000,000


Current Schedule

 Process Date
Project Approval & Environmental Document (M200) June 2023
Right of Way Certification (M410) Fall 2023
Ready to List (M460) Fall 2023
Approved Construction Contract (M500) Spring 2024
Project Completion (M600) Fall 2024


Project Status

The project is currently in Project Approval & Environmental Document (PA&ED) phase.


Project Contact

Caltrans District 10 - Public Information Office
Phone: (209) 948-7977


Title VI Information

The California Department of Transportation (Caltrans) assures that no person shall, on the basis of race, color, or national origin, be excluded from participation in, be denied the benefits of, or be otherwise subjected to discrimination under any program or activity receiving Federal financial assistance, as required by Title VI of the Civil Rights Act of 1964, as amended, the Civil Rights Restoration Act of 1987, and Federal Executive Order 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations).

Caltrans will make every effort to ensure nondiscrimination in all of its programs and activities, whether they are federally funded or not, and that services and benefits are fairly distributed to all people, regardless of race, color, or national origin. In addition, Caltrans will facilitate meaningful participation in the transportation planning process in a nondiscriminatory manner.