Transformational Trucks: Determining the Energy Efficiency Limits of a Class-8 Tractor-Trailer

The report proposes a two-step strategy to improve the efficiency of Class-8 tractor-trailers. Step 1 focuses on technological improvements in aerodynamics, tire rolling resistance, and powertrain efficiency, which could increase fuel economy from 6.5 to 12.3 mpg. Step 2 examines the use of 'turnpike doubles'—long combination vehicles (LCVs) with two 48-foot trailers and a gross vehicle weight rating (GVWR) of 120,000 pounds—to increase freight productivity. Together, these measures could raise ton-mile efficiency by a factor of approximately 2.5, potentially saving 4 billion gallons of diesel fuel and 45 million tonnes of CO2 emissions annually for the U.S. fleet.

• Technological and logistical innovations, excluding hybrid-electric powertrains and auxiliary power units, could increase the ton-mile efficiency of long-haul heavy tractor-trailers by approximately 2.5 times compared to a baseline of 130 ton-miles/gal.
• Implementing the proposed efficiency improvements across the current U.S. Class 8 fleet could result in annual savings of 4 billion gallons of diesel fuel and 45 million tonnes of carbon dioxide emissions.
• Step 1 technological improvements—including integrated aerodynamics, low-rolling-resistance tires, and powertrain optimization—can feasibly increase fuel economy from 6.5 to 12.3 mpg at 60 mph.
• A transformational aerodynamic design incorporating a sealed tractor-trailer gap, full skirting, a rear boat-tail device, and a reshaped cab could achieve a coefficient of drag (Cd) of approximately 0.3.
• The use of wide-base single tires instead of dual tires, combined with advanced rubber compounds, can reduce a typical Class 8 fleet's fuel consumption by 5 percent.
• Reducing the tractive load through aerodynamics and tire improvements allows for a smaller engine; a 300-hp engine with turbocompounding can maintain the same performance on a 2% grade as a baseline 400-hp engine.
• Step 2 proposes the use of 'turnpike doubles' (two 48-foot trailers with a 120,000-pound GVWR), which could increase freight efficiency to 335 ton-miles per gallon.
• The proposed nine-axle turnpike double configuration is more efficient regarding pavement wear than the baseline five-axle combination, carrying 3.8 times more payload per unit of damage on rigid pavements and 3.33 times more on flexible pavements.
• Turnpike doubles are found to be more stable than STAA doubles, with a lower rearward amplification factor (1.28 vs 2.15) and a smaller load transfer ratio (0.52).
• While LCVs may have a slightly higher risk of crashing per vehicle-mile, they are predicted to reduce total fatal crashes because they significantly reduce the total number of tractor-trailer vehicle-miles traveled (VMT).

APA

Ogburn, M., Ramroth, L., & Lovins, A. B. (2008). Transformational Trucks: Determining the Energy Efficiency Limits of a Class-8 Tractor-Trailer. RMI. https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T08-1_RMITransformational_Truck_Study_080709compressed.pdf

Chicago

Ogburn, Michael, Laurie Ramroth, and Amory B. Lovins. Transformational Trucks: Determining the Energy Efficiency Limits of a Class-8 Tractor-Trailer. RMI, 2008. https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T08-1_RMITransformational_Truck_Study_080709compressed.pdf.

Wikipedia

{{cite report |last1=Ogburn |first1=Michael |last2=Ramroth |first2=Laurie |last3=Lovins |first3=Amory B. |title=Transformational Trucks: Determining the Energy Efficiency Limits of a Class-8 Tractor-Trailer |publisher=RMI |date=July 2008 |url=https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T08-1_RMITransformational_Truck_Study_080709compressed.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{ogburn2008transformational, author = {Ogburn, Michael and Ramroth, Laurie and Lovins, Amory B.}, title = {{Transformational Trucks: Determining the Energy Efficiency Limits of a Class-8 Tractor-Trailer}}, institution = {RMI}, year = {2008}, month = jul, url = {https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T08-1_RMITransformational_Truck_Study_080709compressed.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }