A new report from the North American Council for Freight Efficiency (NACFE), presented at TMC 2026 in Nashville, offers one of the most detailed real-world comparisons yet of Class 8 truck powertrains, with diesel reaching 11.5 miles per gallon and a Tesla Semi covering 460 miles on a single charge.
The 277-page operations report is based on NACFE’s 18-day Run on Less – Messy Middle demonstration. It analysed 14 Class 8 tractors powered by diesel, compressed natural gas, battery-electric and hydrogen fuel-cell systems. In total, the study generated 2.2 million lines of data from 73,000 miles of actual freight hauling, challenging a number of long-held assumptions about which technologies are truly road-ready.
Mike Roeth, NACFE’s executive director, said the project aimed to understand where fleets are selecting battery-electric, hydrogen, natural gas, biodiesel and renewable diesel, and how those options fit within real operating environments.
Data was collected every 10 seconds during the September demonstration. NACFE later brought together 26 groups in Boulder, Colorado, for a two-day review, while a panel of major fleets including Amazon, Penske, J.B. Hunt, Covenant and Pitt Ohio evaluated the results.
The 14 trucks represented the full range of Class 8 duty cycles, from long-haul sleeper-cab operations to return-to-base regional work and urban delivery routes as short as 100 miles a day. Roeth said the mix closely mirrors the wider market of 1.8 million to 2 million heavy-duty tractors moving dry vans, reefers and flatbeds across the US.
The study included four diesel trucks, three natural gas trucks, five battery-electric vehicles and two hydrogen fuel-cell units. At Saia’s terminal in Stockton, California, the fleet deployed two Tesla Semis, one for pickup-and-delivery work and the other in a slip-seat arrangement between long-distance less-than-truckload operations and local delivery.
The diesel results stood out sharply. Two of the four diesel trucks achieved 11.5 mpg, while the other two reached 9.5 mpg, far above the national average of 7 mpg, which itself has risen from 6 mpg over the past 15 years. Roeth said that when NACFE talked about 10 mpg during its 2017 Run on Less programme, many in the industry would have thought it was unrealistic. He believes there is still significant fuel economy to be gained from diesel through technology adoption and improved driver performance. Diesel also retains a major infrastructure advantage, with more than 7,500 fuelling stations and unmatched operating flexibility.
The three natural gas trucks in the study used the 15-litre Cummins X15N engine. At Wegmans, they hauled 130,000-pound loads daily across northern New York, one of the toughest duty cycles in the programme. Roeth highlighted three drivers behind renewed interest in natural gas: a purpose-built 15-litre engine, greater availability of renewable natural gas, and better fuelling infrastructure. The natural gas units posted between 4.5 and 6.7 mpg equivalent, though NACFE cautioned that direct comparison with diesel can be misleading because the UPS trucks were pulling doubles and triples and moving substantially more freight. There are now around 1,385 public CNG stations across the US, concentrated in California, Texas and major freight corridors.
Battery-electric trucks showed some of the most striking technological gains. Tesla Semi and Windrose vehicles outperformed Freightliner and Volvo battery-electric models in both charging speed and range. One Saia Tesla Semi completed 460 miles in a day shift on a single charge and then continued making deliveries on a second shift with another driver. Roeth said that performance was achieved at 750 kilowatts, while Tesla is preparing to launch at 1.2 megawatts. He argued that the Tesla Semi demonstrates where battery-electric trucking is heading, with charging for 400 to 500 miles potentially taking just 20 to 30 minutes. NACFE said this is no longer theoretical but already visible in practice. On average, both battery-electric and hydrogen trucks used only 63% of their available range, reflecting infrastructure limitations more than vehicle capability.
Hydrogen remains more constrained. The two Hyundai XCIENT fuel-cell trucks ran efficiently but were held back by limited refuelling access. Penske and Pilot operated those units in Texas and California. Roeth acknowledged that the promise of hydrogen remains difficult to realise at scale. NACFE had to adjust the demonstration after Nikola’s bankruptcy and Hyzon’s difficulties, with only two fleets running Hyundai fuel-cell trucks ultimately taking part.
The report also shows how strongly performance depends on terrain and driver behaviour. Battery-electric vehicles lost more efficiency than diesel on climbs, though they still outperformed diesel on flat routes. Driver technique also proved decisive, both in achieving the 11.5-mpg diesel figures and in maintaining battery-electric efficiency on grades.
NACFE concludes that most fleets are likely to run mixed powertrains in the near term. Operators will need to evaluate each option according to technology maturity, total cost of ownership, duty cycle, infrastructure, regulation, residual value and service support.
At the same time, NACFE is clear about its long-term view. Roeth said the organisation strongly believes battery-electric trucks are the future, arguing that they are simpler, more efficient and less burdened by the complexity and cost that continue to grow around diesel aftertreatment systems. Dean Bushey, NACFE’s director of programmes, agreed and pointed to rapid battery innovation, including new chemistries, lighter packs, possible solid-state cells and faster charging.
NACFE plans to release its emissions report on 15 April, its cost analysis on 1 May ahead of ACT Expo, and its final conclusions in June.
