California appears to have begun a more aggressive enforcement push on diesel-powered transport refrigerated units (TRUs), despite there being no formal announcement and no new regulations on the books.
The last major revision to the state’s TRU emissions framework came in 2022, and the California Air Resources Board’s public guidance does not indicate any recent policy change. At the time of publication, CARB had not responded to media questions on the matter.
The renewed enforcement drive came to light through a client alert circulated by transportation specialists at law firm Benesch. According to the firm, CARB is stepping up pressure primarily on warehouses, which are now being pushed to disclose the TRUs operating at their facilities and verify compliance.
Benesch said the state is ramping up enforcement of rules covering refrigerated trailers, containers and trucks, and that both TRU owners — including operators based outside California — and large facilities receiving refrigerated shipments are being required to register, report and comply.
Brian Cullen, Of Counsel at Benesch and a specialist in California regulatory matters, said the rules have long existed but had not been actively enforced until now.
He noted that California’s broader zero-emission truck agenda, especially under the Advanced Clean Fleets and Advanced Clean Trucks programmes, has largely stalled amid recent disputes with the federal government. The TRU rules, however, remain fully in force and now represent one of the state’s few active regulatory levers in trucking emissions.
The 2022 amendments reaffirmed sweeping changes to the original rule, which dates back to 2004. Among the most significant provisions is the requirement that, starting at the end of 2023, TRU owners must transition at least 15% of their truck TRU fleet operating in California to zero-emission technology each year for seven years, with the goal of reaching 100% zero-emission TRUs by the end of 2029.
Cullen said that, in practice, there has been a near-complete halt in companies attempting to buy zero-emission TRUs.
What is changing now is the level of responsibility being placed on facilities. Cullen said companies have reported receiving notices reminding them that information must be submitted quarterly, effectively pushing warehouses to identify carriers whose refrigerated trailers do not display the required compliance labels.
Under California law, all diesel-powered TRUs operating in the state must be registered in the Air Resources Board Equipment Registration system, obtain a CARB Identification Number and display CARB compliance labels renewed every three years. Owners must also pay operating fees that help fund enforcement.
Since the start of 2024, owners of refrigerated warehouses or distribution centres larger than 20,000 square feet, grocery stores larger than 15,000 square feet, seaport facilities and intermodal railyards with TRU activity have also had to register with CARB, pay fees every three years and either report all TRUs operating at their facilities on a quarterly basis or ensure only compliant units enter their sites.
Compliance also extends beyond labels. Diesel TRUs must use refrigerants that meet specific global warming thresholds and engines that comply with stricter particulate matter standards. That means warehouses may now need to determine whether the units using their premises comply with the state’s emissions rules.
Benesch warned clients that businesses should verify their TRUs are properly registered and labelled and that facilities are meeting reporting or compliance declaration obligations. The firm said proactive compliance is essential to avoid costly fines and disruptions to refrigerated supply chains.
Those fines can reach up to $10,000 per day.
Glen Kedzie, principal at E&E Strategies, said the rules could eventually face legal scrutiny under the Commerce Clause, given that they affect operators based beyond California’s borders. He questioned whether the state can require an Ohio trucking company, for example, to maintain records and submit them in order to obtain compliance stickers before entering California.
Jason Massey, whose company Ndustrial offers an electric alternative to diesel-powered TRUs, said the standards warehouses are most likely to focus on now are those linked to particulate matter and refrigerants, given that fleet conversion to zero-emission technology no longer appears to be the immediate priority.
Massey added that interest in electric alternatives has not disappeared. He said adoption remains strongest at single-company sites, such as food distributors operating dozens or even hundreds of trailers in one location, where cutting emissions and reducing noise makes the switch more attractive. He also noted that concerns over eventual compliance never really disappeared, particularly given the scale of potential penalties.
