I-5/SR-78 Interchange Project

Concepts to improve the Interstate 5 (I-5)/State Route 78 (SR-78) interchange in the cities of Oceanside and Carlsbad in San Diego County are currently being evaluated by Caltrans. Currently, motorists experience traffic delays at the interchange where there is a lack of direct freeway-to-freeway connections. These connections are currently made via a traffic signal at the I-5 southbound ramps/Vista Way intersection.

Project Objectives

  • Improve traffic operations within the project area for local motorists, increase interchange capacity and improve overall air quality by reducing idling vehicles.
  • Reduce travel times and congestion through the interchange for local and regional commuters.
  • Provide carpool/HOV and transit vehicle connectivity between two important regional transportation corridors.
  • Protect and/or enhance the human and natural environment in the project vicinity, such supporting the Buena Vista Lagoon Restoration, where feasible.

Potential Interchange Improvements

  • Adding direct freeway-to-freeway connectors from southbound I-5 to eastbound SR-78 and westbound SR-78 to southbound I-5.
  • Building direct access ramps that connect to future carpool and transit vehicle lanes on I-5 and SR-78.
  • Reconfiguration of the existing interchange to accommodate the new connections outlined above.

Project Schedule

  • Preliminary Planning: 2012-2021

  • Environmental: 2024-2029
    • Public Engagement: Summer/Fall 2024
    • Traffic Pattern Studies Summer/Fall 2024
    • Environmental Impact Report/Environmental Impact Studies (EIR/EIS) expected to be complete by 2029.
  • Design 2029-2032 (pending funding)
  • Construction 2033-2037 (pending funding)


The proposed I-5/SR-78 Interchange Project is federally funded for the initial planning and environmental efforts. $8 million is available for Preliminary Design and Environmental Studies for 2024-2029. Over the next few years as project alternatives are refined, additional funding will need to be identified for Design and Construction. 

To stay up to date with SR-78 projects, please visit sandag.org/subscribe to sign up for updates. 

For any questions or comments on projects on the SR-78 corridor, please contact the project team by emailing SR78@KeepSanDiegoMoving.com, and a team member will respond to you promptly.