Transportation sources accounted for approximately 40% of all GHG emissions in the US in 2006; medium- and heavy-duty vehicles (above 8,500 gross vehicle weight rating) represent about 22% of the transportation emissions, up from 15 percent in 1990, according to the EPA. Trucks therefore are an important place to look for energy savings and climate change mitigation in the transportation sector.

Among medium- and heavy-trucks, Class 8 trucks are the largest CO₂ emitters and fuel users, consuming two-thirds of all truck fuel, or 1.57 million barrels per day. Current fuel economy for Class 8 trucks is estimated by the US Department of Energy at 6.0 mpg and projected to rise modestly to 6.8 mpg by 2025 (EIA, 2009). Substantial improvements could be made to truck efficiency through a variety of existing and emerging technologies, including engine improvements, transmission enhancements, better aerodynamics and changes in systems and logistics.

This study finds that fuel consumption for new tractor-trailers could be lowered by 20 percent starting in 2012 and as much as 50 percent beginning in 2017, while providing net savings for the owner based on lifetime fuel savings paying for the incremental vehicle, operation, and maintenance costs.

The project was directed by an steering committee comprising representatives from major truck and powertrain manufacturers, government agencies, trucking fleets, and fuel economy and heavy-duty experts from non-profit organizations. The core of the analysis consisted of a series of modeled simulations.

Once the baseline truck and engine was determined (Volvo D13 (2010 emissions), Kenworth T600, 10-speed manual transmission), two simulation models were used to allow the evaluation of various packages: GT-POWER for engine cycle simulation and RAPTOR to model the vehicle, including the transmission and driveline. Southwest Research Institute (SwRI) was engaged to perform the vehicle and engine simulation modeling

For the test cycle, SwRI modified the California Heavy-Duty Diesel Truck Drive Cycle by increasing the portion of high-speed driving to reflect longer average travel distances nationwide; increased speed by 8% to reflect current long-haul operating speeds; and added two segments with positive and negative grade (1% and 3%). The results are specific to long-haul trucks.

However, substantial reductions in heavy-truck greenhouse gas emissions can be achieved. The NESCCAF-ICCT study shows that by 2017 with the introduction of technologies in development or currently in production as much as 40% of fuel consumption and greenhouse gas emissions from heavy trucks hauling freight can be reduced. If vehicle weight and length are also increased, the savings can reach 50%.

A total of 32 technologies and operational measures were identified and considered for inclusion. The technologies examined fell into five primary categories:

1. off-the-shelf aerodynamic improvement technologies;
2. off-the-shelf drivetrain technologies;
3. emerging drivetrain technologies;
4. emerging aerodynamic improvement technologies; and
5. operational measures.

SwRI did not consider technologies that are not currently in production or for which a design specification is not available in the literature; as a result there is likely additional potential for reduction with more advanced technologies yet to be as developed.

After initial screening, SwRI assembled a series of 14 technology packages for modeling. The net cost analysis assumed an average price of $2.50 per gallon of diesel fuel, and assumed that the annual mileage declines as the vehicle ages.

The study found that eight building block technologies considered (SmartWay 2007 (SW1); Advanced SmartWay (SW2); Parallel hybrid-electric powertrain (HEV); Mechanical turbocompound; Electric Turbocompound; Variable Valve Actuation (VVA); Bottoming cycle; and Advanced EGR) delivered a range of potential reductions ranging from the very modest to up to almost 28% for a host of aerodynamic, friction and rolling resistance technologies called Advanced Smartway. Combined, these existing and emerging technologies are capable of improving the baseline fuel consumption up to 50%.

Despite the wide range in costs, the report notes, most of these technologies pay for themselves in the first few years of ownership with the exception of the hybrid electric powertrain.

With aggressive introduction of these technologies and operational measures into the US truck fleet, this study found that by 2030 an estimated 8 billion gallons of diesel fuel and 97 million tons of the CO₂ could be saved annually, with lesser reductions being achieved as soon as 2012. This would be equivalent to removing 2 million cars from the road for one year. This is also equivalent to the amount of CO₂ emitted from 20 coal-fired power plants in a year.

Cumulative CO₂ emissions avoided between now and 2030 would equal approximately 1.1 billion metric tons, or the equivalent of removing 20 million cars from the road for one year.

Over a three year period and with a diesel fuel price of $2.50 per gallon, this study found that five of the technology packages would result in a net cost savings to the truck owner, taking into account both incremental technology costs and fuel savings.

The analysis shows that most of the technology combinations that provide the greatest reductions would not be adopted into the fleet assuming a three-year payback requirement. This indicates that given the short payback period demanded by the trucking industry, a number of these technologies will not be adopted into the US fleet absent regulation. With a longer payback period of 15 years estimated lifetime net savings are between $30,000 and $42,000 for owners of vehicles achieving CO₂ and fuel consumption reductions of up to 50 percent.

Resources

• Reducing Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO₂ Emissions