Why the EPA needs to hear from the motorcoach industry about derate rule

If you have a story about an unpleasant experience related to the U.S. Environmental Protection Agency’s derate rule, the federal agency wants to hear from you by May 16.

The EPA is proposing new, stronger standards to promote clean air and reduce pollution from heavy-duty vehicles and engines starting in model year 2027. 

The proposed standards would reduce emissions of smog- and soot-forming nitrogen oxides from heavy-duty gasoline and diesel engines and set updated greenhouse gas standards for certain commercial vehicle categories.

This proposed rule would ensure the heavy-duty vehicles and engines – including motorcoaches –  that drive American commerce and connect people across the country are as clean as possible while charting a path to advance zero-emission vehicles in the heavy-duty fleet.

Requirements for Diesel Exhaust Fluid (DEF) have resulted in manufacturers designing engines with a 5 mph final inducement speed that generally occurs after four hours. 

Examining the data

“We received many comments … that the reasons these trucks and buses are going into inducement are a lot of times unrelated to keeping high-quality DEF into the system,” said the EPA’s Amy Kopin. “Once that vehicle hits that final, severe inducement, it generally would have to be towed, and you’d have to have a special OEM scan tool to get it out of that stage.”

Kopin is an engineer from the EPA’s Heavy-Duty Onroad and Nonroad Center Assessment and Standards Division Office of Transportation and Air Quality. The group writes regulations

She added that she was part of a team gathered to review the data compiled since the Selective Catalytic Reduction System went into effect. The goal is to make sure folks use “high-quality DEF, but we also want to discourage tampering.”

Kopin joined the United Motorcoach Association Town Hall on May 5 to review the current proposed rulemaking to “improve serviceability of heavy-duty vehicles and engines” beginning with model year 2027 under EPA’s Clean Trucks Plan. These rules for heavy-duty engines include motorcoaches.

Phil Streif with Vandelia Bus Lines

The core of the proposed rule is to establish more stringent criteria pollutant standards (including nitrogen oxides, particulate matter, hydrocarbons, and carbon monoxide) for heavy-duty engines beginning in model year 2027 and strengthening the Phase 2 greenhouse gas standards for model year 2027 and beyond.  

Perhaps more important to the motorcoach industry, the proposal includes targeted provisions to help ensure that owners can efficiently maintain emissions performance over the life of the engine, including enhanced communication with operators, updated diagnostic requirements, a revised inducement (engine derate) policy for SCR-based after-treatment systems, and improved access to service information.

“Back in 2009, when we had our original guidance on this, the intent was to keep these triggers to things that operators could control. So they’re supposed to make sure you use DEF, that it’s high-quality DEF, that the system is flowing and that you’re not tampering,” said Kopin, noting that the agency had a lot of comments indicating those aren’t issues any longer. “It’s really morphed beyond that, so what we’re proposing is a specific set of triggers.”

Complaints from industry

Phil Streif, of Vandalia Bus Lines in Caseyville, Illinois, who has been an industry advocate, argues that EPA’s current derate schedule of slowing a bus to 5 mph within four hours when the vehicle has certain emission codes is not adequate time for anyone to troubleshoot or fix the issue. It also threatens passenger safety because slowing the bus down to 5 mph on the interstate could result in a rear-end collision. 

Instead of derating to 5 mph four hours after a trigger, the EPA is proposing that the derate schedule would be implemented over 60 hours with four steps down, she said. 

The EPA is seeking comments from motorcoach company representatives regarding the hardships incurred by derates, including tow bills, displacing passengers, cost to dispatch or acquire another coach, missed activities, etc.

Kopin suggested that commenters be specific about the impact of the rules on their business.

For example, Tom Giddens, owner of Pacific Coachways and UMA Board Member, said a faulty sensor resulted in shutting down one of his coaches while in the middle of a tour in Arizona.

“We had a group get shut down in Kingman for a faulty sensor,” Giddens said. “The bus was towed back to Las Vegas. Group had to wait for a replacement bus from Las Vegas. A week later, we picked up the bus at the dealer and didn’t make it out of Las Vegas and the new sensor failed. The third one worked fine.” 

To see Kopin’s entire presentation, UMA Members can watch a recording of the May 6 UMA Town Hall.

The public can access the rule, supporting documents and comments here, and the proposal here.


Serviceability proposals: see Section IV.B.3.

Inducement proposal: see Section IV.D.

OBD proposal: see Section VI.C.1.iii.

Comments may be filed through May 13 here.

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