I-5/SR 78 Interchange Project

bv lagoon
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; and
  • 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 being studied include:

  • 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; and
  • Reconfiguration of the existing interchange to accommodate the new connections outlined above.

Environmental Review Process

In 2014, Caltrans began studying various options to improve the interchange. More than 20 options were analyzed as part of the preliminary feasibility study. Caltrans hosted a public workshop on January 29, 2015, at the Carlsbad Senior Center, to gain initial feedback from members of the public about the project.


In September 2019, the SANDAG Board of Directors programed partial funding for the environmental review process for the I-5/SR 78 Interchange. This funding is programmed for 2023, at which time a public scoping meeting and formal public comment period will formally kick-off the environmental review process. The Environmental Impact Report/Environmental Impact Studies (EIR/EIS) is expected to be complete by 2028.  Funding has not been secured for design or construction at this point in time.  

Key Documents

sr 78 fact sheet    I-5/SR-78 Interchange FAQ    Jan. 29 Public Workshop Displays
public workshop displays
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