Understanding Indirect Source Rules (ISRs): Managing Emissions from Warehouses and Freight Operations
As air pollution and its health impacts continue to draw increased regulatory attention, several U.S. states have introduced Indirect Source Rules (ISRs) targeting emissions linked to warehouses and their associated vehicle traffic. These rules are designed to reduce air pollution from heavy-duty trucks, transport refrigeration units (TRUs), yard trucks, and other mobile sources serving warehouse facilities.
Unlike the Advanced Clean Trucks (ACT) rule, ISRs do not require U.S. EPA approval, giving states more flexibility to address localized air quality challenges—particularly in overburdened or disadvantaged communities.
The Rise of State-Level ISR Programs
California pioneered the ISR model through the South Coast Air Quality Management District’s (SCAQMD) Warehouse Actions and Investments to Reduce Emissions (WAIRE) Program, which seeks to lower nitrogen oxides (NOx) and particulate matter (PM) emissions from freight operations. Other states—Colorado, New York, and New Jersey—have since proposed or developed similar frameworks aimed at curbing indirect emissions from logistics and distribution centers.
Key State ISR Frameworks and Requirements
California
SCAQMD’s Rule 2305 (WAIRE Program) applies to warehouses with 100,000 square feet or more of indoor floor space located within the South Coast Air Basin.
Operators must:
- Track emissions associated with truck trips to and from their facilities.
- Earn WAIRE Points by completing emission-reducing actions or pay mitigation fees.
Qualifying activities include:
- Using zero- or near-zero-emission trucks.
- Installing on-site solar power or charging infrastructure.
- Electrifying yard equipment and TRUs.
The rule focuses on reducing diesel PM and NOx emissions, particularly in areas facing environmental justice concerns. Compliance is mandatory for all qualifying warehouses.
Colorado
The Regional Air Quality Council (RAQC), responsible for air quality planning in the Denver Metro/North Front Range nonattainment area, is developing ISRs modeled after California’s approach. These proposed regulations would require warehouse operators to reduce or offset emissions associated with freight traffic—either through direct emission reductions or mitigation fees. The objective is to improve air quality in urban freight corridors and advance Colorado’s climate and health goals.
New York
The New York State Senate Bill S1180A (2025) proposes an ISR regulating emissions from vehicles associated with large distribution warehouses. Under this framework, warehouse operators would be required to demonstrate proactive emission reduction efforts, including:
- Installing solar panels or charging stations.
- Transitioning to zero-emission trucks and equipment.
- Reporting emissions data to state authorities.
New Jersey
New Jersey’s proposed Warehouse and Port Pollution Reduction Act (WPPRA)—Senate Bill S3546—aims to mitigate pollution from logistics operations statewide. The rule would hold warehouse operators accountable for reducing diesel emissions from trucks and TRUs serving their facilities. Like other ISR models, it prioritizes relief for overburdened communities disproportionately affected by freight-related pollution.
ISR Compliance: Menu-Based or Points Systems
Most ISRs employ a menu-based or points-based compliance system, allowing warehouse operators to choose from a range of approved actions to meet emission-reduction obligations.
Common compliance pathways include:
- Transitioning to Low- or Zero-Emission Trucks and Yard Vehicles
Reduces NOx and PM emissions from diesel engines. - Installing On-Site Renewable Energy and Efficiency Upgrades
Solar installations, energy-efficient retrofits, and zero-emission charging or fueling infrastructure can all earn compliance credits. - Paying Mitigation Fees
Facilities may offset their emission obligations by funding community-based clean air projects or zero-emission truck incentives. - Developing Custom Compliance Plans
Warehouses may propose site-specific strategies tailored to their operational profiles and freight activity.
Focus on Transport Refrigeration Units (TRUs)
TRUs represent a significant—and often overlooked—source of diesel particulate emissions at warehouses. Warehouses can make meaningful progress toward ISR compliance by requiring all visiting refrigerated trailers to use:
- Low-emission TRUs from OEMs, or
- Certified Diesel Particulate Filters (DPFs), such as Rypos active DPF systems.
By capturing harmful soot before it’s released, DPFs substantially reduce local exposure to diesel particulate matter and help warehouses earn ISR compliance points or reduce mitigation fees.
Incorporating TRU emission reductions into ISR compliance strategies not only supports regulatory adherence but also improves community air quality, enhances sustainability credentials, and supports the broader transition to clean freight technologies.
Summary
Indirect Source Rules represent a growing trend in state-level air quality regulation—requiring warehouses to take responsibility for the indirect emissions generated by their freight operations.
For operators, understanding these programs and taking early action—especially by addressing TRU emissions through DPF retrofits or low-emission technologies—can deliver both compliance and environmental benefits.
Warehouses that proactively implement emission reduction strategies not only avoid costly mitigation fees, but also demonstrate leadership in sustainable logistics and contribute to cleaner air for surrounding communities.
To learn more about low-emission TRU solutions or to develop a custom emissions reduction program, contact Rypos. As recognized for decades by the California Air Resources Board, reducing emissions from TRU) delivers near-term, measurable improvements in local air quality by cutting diesel particulate matter and NOx emissions—directly improving community health outcomes and reducing climate impacts.
