Senate EPW hearing spotlights safety risks from diesel ‘derates’ in Alaska and debate over statutory exemptions

The Senate Environment and Public Works Committee heard testimony on S.3135, the “Cold Weather Diesel Reliability Act,” at a hearing focused on diesel exhaust fluid (DEF) system failures that can trigger automatic engine “derates” and immobilize trucks and equipment in extreme cold.

Supporters, led by Sen. Dan Sullivan, said the bill would allow targeted manufacturer overrides or regulatory adjustments in defined cold-weather conditions so vehicles and heavy equipment do not lose power when operators are far from help. "When that happens in a remote area, it becomes a serious safety risk," Sullivan said, recounting a trucker on the Dalton Highway who crawled at about 5 miles per hour during a blizzard and required a tow that cost about $15,000.

Why it matters: modern selective catalytic reduction systems reduce NOx by injecting DEF into exhaust, but sensors and pumps can malfunction or DEF can freeze. Committee witnesses described cases in Alaska in which derates sidelined snow-removal gear, ambulances, school buses and freight trucks — failures that can delay emergency response and interrupt supply lines in places with long distances between service and fuel points.

Alaska DOT Commissioner Ryan Anderson told senators his department has seen emissions-control problems become the single largest source of maintenance failures in its diesel fleet. "Our fleet director estimates that 70 to 80% of diesel engine maintenance issues over the past two years are related to emissions-control systems," Anderson said, adding that on any given day 10% to 30% of heavy equipment may be unavailable because of such faults.

Farm-sector testimony: Todd Thornstrom, a fourth-generation farmer, said agricultural operators have faced increased costs and operational disruptions tied to DEF systems and sometimes avoid purchasing newer equipment because of reliability concerns. "If [a tractor] goes into the derate mode, you won't be able to run your grain cart like you're wanting to," Thornstrom said, describing a scenario that can halt harvest.

Environmental concerns: John Walke, director for clean air programs at the Natural Resources Defense Council, opposed a statutory exemption and urged resolving the issue through the EPA’s rulemaking and oversight processes. Walke said EPA has directed manufacturers to update software and asked manufacturers for data on DEF-system failures, and he cautioned S.3135 could be read to allow broad exemptions nationwide. "I urge Congress not to start here," Walke said, warning that a statutory carve-out risks undermining nationwide NOx protections.

Committee debate: Members split on whether a legislative fix is necessary. Ranking Member Sen. Sheldon Whitehouse framed the hearing in a broader context of recent EPA rollbacks and stressed the public-health harms of NOx; sponsors such as Sen. Sullivan and Sen. Cynthia Lummis said the issue is distinct and urgently affects public safety in remote, cold regions. Senators pressed witnesses on frequency of incidents, economic impacts, and whether administrative fixes at EPA are sufficient.

What's next: Committee members may submit written questions; senators set a deadline for questions and witness responses. The hearing record will include submitted written testimony from state and local fire chiefs and industry groups. The committee adjourned without a vote on the bill.

The hearing transcript and the witnesses' written statements will be the primary sources for any subsequent markup or legislative language revisions.