Ocean-Going Vessel In-Transit Rule

⚠︎ STATUS: IN DEVELOPMENT

Quick facts

  • 95%

    of ship emissions happen while a vessel is moving, not docked

  • 2037

    ocean-going vessels projected to become one of CA’s largest mobile pollution sources by this year without action

  • 5-7 years

    CARB’s estimated timeline for the full rule-making process

What this policy would do

California currently has no rule governing pollution from ocean-going vessels while they are moving through state waters. The proposed In-Transit Rule would fill that gap by addressing emissions from ships along California’s coast and shipping corridors — where approximately 95% of ship emissions occur.

Potential measures include:

  • Cleaner engines: Requirements for newer, lower-emission vessels
  • Alternative fuels: Incentives or requirements for cleaner fuels, including methanol and other alternatives
  • Operational changes: Measures such as reduced vessel speeds in designated areas
  • Future zero-emission technologies: A framework that can support California’s transition toward zero-emission ocean-going shipping

A strong in-transit standard would complement California’s existing rules for ships at berth and commercial harbor craft, addressing a major source of ship pollution that those regulations do not cover.

  • Coastal communities along California’s shipping corridors — not just those next to ports
  • Port communities already affected by At-Berth and harbor craft pollution, since in-transit emissions compound existing exposure

Where things stand

CARB is currently developing the In-Transit Rule through workshops, technical research and community engagement.

What’s happening: CARB is developing the rule through technical research, public workshops and community engagement.

  • Late 2024: CARB began formal work on the rule.
  • February 2026: A CARB workshop included preliminary findings from a UC Irvine assessment of emissions-control technologies.
  • 2024 research: Pacific Environment and UC Berkeley’s Goldman School of Public Policy released research that helped support CARB’s commitment to develop the rule.
  • Ongoing: CARB is evaluating potential emissions-control strategies and gathering input from communities and stakeholders.

The opportunity: The rule is still being shaped. Pacific Environment is pushing for a strong final standard that delivers meaningful emissions reductions, incorporates community input and creates a clear path toward zero-emission ocean-going shipping.

Why it matters

  • Cleaner air along California’s coast

    Ocean-going vessels emit pollution throughout their journeys along California’s shipping corridors — not just when they are docked. In-transit emissions can affect coastal communities far beyond traditional port neighborhoods.

  • The largest share of ship pollution

    Approximately 95% of ship emissions occur while vessels are in transit, making moving ships a critical source of pollution that California’s existing regulations do not fully address. Without additional action, ocean-going vessels are projected to become one of California’s largest mobile pollution sources by 2037.

  • A path toward zero-emission shipping

    A strong in-transit rule can help accelerate cleaner marine technologies and support Pacific Environment’s goal of zero-emission ocean-going shipping in California by 2040.

Take action

Stay informed on California’s clean shipping future

California is developing new policies to reduce pollution from ocean-going vessels and move toward zero-emission shipping. Sign up for updates on the In-Transit Rule, the latest clean shipping developments in California and beyond and opportunities to make your voice heard.

Sign up

Timeline & key dates

2022
CARB identifies need for further reductionsCARB’s Interim Evaluation finds that additional emissions reductions are needed, particularly from ocean-going vessels while in transit.
2024
Research supports stronger actionPacific Environment co-releases decarbonization research with UC Berkeley’s Goldman School of Public Policy.
2024
CARB announces rulemaking kickoffCARB begins formal work toward developing an in-transit emissions rule.
2024
First public workshopCARB begins gathering input on potential approaches and emissions-control strategies.
2026
Technology assessment updateCARB shares preliminary findings from a UC Irvine assessment of emissions-control technologies.
2026
Community engagement survey closesCARB accepts responses to its community engagement survey as part of the rulemaking process.

How long will this take? CARB estimates the full rulemaking process could take five to seven years.

Frequently asked questions

No — CARB is still developing it. This page will update as the rulemaking moves forward.
CARB estimates five to seven years from start to finish.
The strength of the final rule depends on public input now, while CARB is still shaping it — not after it’s finalized.
Those rules cover ships while docked or operating within harbors. This one would cover ships while they’re actually moving through California’s coastal waters — the source of most ship pollution.

Learn more about the In-Transit Rule

Want to learn more about California’s proposed Ocean-Going Vessel In-Transit Regulation? Visit CARB’s program page for the latest information on the rulemaking process, technical assessments, workshops and other developments.

Go to CARB website

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