LAS VEGAS — The Trump administration may have the revoked greenhouse gas (GHG) rules, but student transportation fleets are still barreling toward a major emissions change that will reshape diesel engine technology, maintenance practices and purchasing strategies as soon as Jan. 1, 2027.
That was the clear message from engine and truck executives during Monday’s ACT Expo roundtable, “What the Final Rule Means for Fleets, OEMs & Suppliers.” Cummins and International leaders urged fleets to prepare now for the new low nitrogen oxides (NOx) rules — and not be lulled into complacency by headlines regarding greenhouse gas (GHG) rollbacks.
GHG Push Eases, but NOx Crackdown is Full Speed Ahead
David Hillman, vice president of integrated technology sales at IC Bus parent company International, told attendees that many fleets still misunderstand the regulatory landscape. He said fleets often assume that because federal GHG actions were rescinded, tailpipe rules are off the table. That, he warned, is wrong.
He urged fleets to separate climate-focused GHG policy from criteria pollutant rules such as NOx. The federal GHG “endangerment” framework — which effectively pushed manufacturers toward battery-electric vehicles by requiring rapid fuel-efficiency gains — has been set aside.
But the EPA’s low-NOx rule remains, added panelist Andrea Lukas, the director of product management for the North American on-highway business at Cummins
“We’ve heard from high-level officials at EPA that’s sticking, so we need to prepare for that now,” she said.
The upcoming federal standard will tighten heavy-duty NOx limits to 35 milligrams, or 0.035 g/bhp-hr, starting Jan. 1. Hillman described the change as an approximately 80 percent reduction in NOx compared with current levels. That shift is substantial, even though the core diesel technology path of diesel oxidation catalysts, diesel particulate filters and selective catalyst reduction aftertreatment will remain largely familiar.
For school buses, that means diesel is not going away anytime soon, but the next generation of engines will be more complex, more tightly controlled and, almost certainly, more expensive.
“Speaking for International, we’ve been fairly direct that we are we’re very bullish on diesel … it’s hard to beat the efficiency of the diesel combustion cycle … diesel’s got a very enviable track record in position,” Hillman added. “I think it’s reasonable to expect diesel efficiency to still be applicable into the 2040 and beyond realm.”
Costs Less Than Early Numbers but Still Higher
A year to 18 months ago and even at the STN EXPO East conference in March, many fleets heard dire projections about price spikes for 2027-compliant vehicles. Hillman explained those early figures assumed not only new hardware but also much longer federal emission warranty and “useful life” requirements — in some proposals, up to 10 years.
He said roughly half of the anticipated price increase was tied to added hardware and design changes, while the other half came from extended emission warranties and the costly validation work to ensure engines would still meet the 35 mg NOx limit a decade after production.
More recent signals from EPA suggest warranty and useful-life requirements may revert closer to today’s norms, such as five years or 100,000 miles in the heavy-duty space. If that holds in the final rule, Hillman said fleets can roughly “cut in half” some of the largest price increases they heard discussed last year.
Still, the technology required to hit 35 mg NOx rule has its costs. Student transportation directors should budget for higher acquisition costs for 2027 and newer diesel buses, even if the final price tags fall short of the early worst-case scenarios. Exact numbers will not be clear until the EPA’s rulemaking language is finalized.
Fuel, DEF and Performance: Less Disruption than 2007, 2010
On performance, both Cummins and International stressed that fleets should not expect the kind of fuel-economy and drivability disruptions seen in the 2007 and 2010 emission changeovers.
Lukas said the focus is now building on mature architectures rather than introducing unproven concepts. Larger catalysts, new heating strategies to address cold-start NOx, and packaging changes are being paired with redesigned, lighter engine blocks and combustion improvements.
Lukas said Cummins is targeting fuel efficiency improvements on its new platforms and weight neutrality once lighter engine components and larger aftertreatment systems are balanced. She also said the company aims to keep diesel exhaust fluid (DEF) consumption in a similar range to today’s levels.
“We are utilizing a belt‑driven alternator, so pretty simple technology on the engine, and so that powers heaters in the aftertreatment … trying to simplify it as much as possible by using known designs,” she explained.
Hillman said International’s S13 powertrain is engineered to be fuel-economy neutral and weight neutral with the 2027 regulations in most applications. He expects DEF consumption to rise modestly — on the order of one percentage point relative to fuel, rather than a dramatic jump.
For school buses, that could mean routing, refueling infrastructure and gross vehicle weight ratings may not require wholesale redesigns. Instead, DEF logistics and range assumptions should be revisited once final product specifications are known.
Emissions Training and Tools
One message that came through clearly for maintenance managers: Training cannot wait.
Lukas said Cummins will begin rolling out technician training for 2027 products over the next one to two months, with materials pushed through OEM and dealer channels. She urged fleets to take every available opportunity to get technicians trained early, especially around new service tools.
For fleets running Cummins-powered trucks and buses, one major shift will be the retirement of Cummins Insight on the model-year 2027 and beyond fuel-agnostic HELM platforms. Instead, Cummins will rely on Guidanz as its primary diagnostic and service interface, with expanded digital capabilities, including portals, over-the-air diagnostics and remote calibration updates.
International, which carries over roughly 90 percent of the hardware in its S13 powertrain from current products, expects less disruption in its own toolchain. But Hillman echoed Lukas on the need for ongoing technician and driver training to keep pace with more sophisticated electronics and emissions controls.
Don’t Wait on Pre-Buys
Hillman and Lukas also warned that the back half of 2026 is likely to be production-constrained, as fleets across multiple sectors pull forward purchases to avoid first-year 2027 NOx rule pricing and complexity. This year’s State of Sustainable Fleets report unveiled Monday at ACT Expo stated that manufacturers are already selling out new build slots for the third and fourth quarters of 2026.
While the panelists said they do not expect a pre-buy on the scale of 2007 or 2010, both Cummins and International anticipate enough “front-loading” of demand to stress supplier capacity. In practice, that means school bus orders for the 2026–2027 school year could compete with a crowded market, especially for certain configurations.
Article written with the assistance of AI session transcript.
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