Sustainable Vehicle Practices

 

Tractor Aerodynamics  |  Trailer Aerodynamics  |  Tires  |  Engines  |  Alternative Fuels
Cargo Management  |  Higher Productivity Vehicles

truck-on-road-3Truck manufacturers first began to develop more fuel efficient vehicles in the 1970s as a result of the energy crisis. Since that time, significant gains in efficiency have been made through improvements in aerodynamics, tire rolling resistance and engine performance.  Manufacturers have enhanced tractor aerodynamics, for example, by streamlining the front profile and sloping the hood, utilizing aerodynamic bumpers and mirrors, and adding roof and side fairings.  These changes have reduced the average drag coefficient (a measure of wind resistance) from 0.80 to 0.65 – a 20 percent improvement compared to more traditional tractor styling.[5]  Other advances such as trailer aerodynamics, innovative cargo management systems and higher productivity vehicles also have the ability to improve fuel efficiency and reduce emissions.

Further efficiency improvements have been mandated for medium- and heavy-duty vehicles manufactured in 2014 and beyond.  The U.S. Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration (NHTSA) issued a joint rulemaking in 2011 that specifies emissions and fuel consumption standards, respectively, for truck-tractors, heavy-duty pickups and van and certain vocational vehicles.[6]  Phase 2 of this program is currently under development and will build upon the initial requirements. A Notice of Proposed Rulemaking (NPRM) is expected by March 2015 followed by a final rule in March 2016 affecting vehicles manufactured in 2020 and beyond.

Tractor Aerodynamics

Truck tractors have become increasingly more aerodynamic with manufacturers analyzing design aspects ranging from windshield angles to sun visor shapes in an effort to improve efficiency.  Several devices are currently available for improving tractor aerodynamics including roof fairings, gap reducers, aerodynamic bumpers and mirrors and fuel tank side fairings (see Figure 4).

Figure. Currently Available Aerodynamic Devices

Figure 4. Currently Available Aerodynamic Devices

Many of these devices are available as options on new tractor purchases or can be retrofitted on existing tractors.  According to the National Academy of Sciences, a roof fairing can reduce fuel consumption by 7 to 10 percent at a cost of $500 to $1,000 per unit while a gap reducer may decrease fuel consumption by 2 to 3 percent at a cost of $300 to $500.[7]  A separate study found that traditional mirror designs account for 4.5 percent of the total vehicle drag while aerodynamic mirrors account for only 1.5 to 2.5 percent. [8]  Switching from the traditional mirror design to the aerodynamic option resulted in a 1 percent improvement in fuel economy.[9]
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Trailer Aerodynamics

While significant fuel efficiency improvements can be made through increasing tractor aerodynamics, changes made to the trailer can yield additional gains.  EPA’s SmartWay Partnership, for example, has researched the impact of several trailer modifications, including side fairings (also known as a “skirts”), which are attached to the lower edge of each trailer side between the axles and trailer tails (also known as “boat tails” or “base flaps”) which are attached to the rear door of the trailer (refer to Figure 4).skirt

Trailer side fairings typically range in cost from $700 to $1,100 and have been estimated to improve fuel economy by 3 to 7 percent.[10]  Side fairings are more commonly used in higher speed, long-haul operations since they can be less effective and have greater potential for damage in lower speed, urban environments.  Trailer tails are another option, ranging in cost from $1,000 to $1,600 while having the potential to improve fuel economy by 3 to 5 percent.[11]
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Tires

Another important factor in truck fuel efficiency is tires.  Tire rolling resistance accounts for approximately 30 percent of the energy required to move a line-haul truck on level roads and at highway speeds.[12]

Low Rolling Resistance Tires

Low rolling resistance tires are designed to minimize the friction between the roadway and tire. tireSpecific features may include slightly thinner sidewalls, shallower tread depths and low rolling resistance tread compounds.  A number of trucking companies have publicized using low rolling resistance tires on at least a portion of their fleet, including Con-way Truckload, C.R. England, Penn’s Best, Spirit Truck Lines and U.S. Xpress.[13]  According to the National Research Council, low rolling resistance tires can provide a 3 – 6 percent reduction in fuel consumption.[14]  The approximate per tire cost of $265 is comparable to conventional tires.[15]  However, due to the potential for faster tread wear-out, purchasers need to evaluate the cost-benefits of increased tire costs versus lower fuel costs.

Single-Wide Tires

Single-wide tires (also known as “wide-base” or “super-singles”) can improve fuel efficiency by an additional 1 – 1.5 percent compared to LRRTs.[16]  Single-wide tires use a single rim with only two sidewalls to replace the conventional dual tire configuration which utilizes two complete tires (i.e. two rims and four sidewalls).  Single-wide tires therefore offer the added benefit of weight savings.  A five-axle tractor-trailer combination that is equipped with single-wide tires and aluminum rims (which are lighter than standard steel rims) can reduce weight by approximately 750 pounds.[17]  The cost of equipping a tractor and three accompanying trailers has been estimated to range from $3,600 – $4,480.[18]

Tire Pressure Systems

Under-inflated tires can significantly increase rolling resistance, thus increasing fuel consumption. The Federal Motor Carrier Safety Administration recently evaluated the effectiveness of tire pressure monitoring systems (TPMS) and automatic tire inflation systems (ATIS).[19]  The two motor carriers involved in the field test reported a fuel economy increase of 1.4 percent using the systems.  The payback period for these systems, which have a cost of approximately $1,500 per tractor-trailer, was found to range from less than 14 months to less than 6 months for a high-mileage fleet.  An earlier report prepared by the North American Council for Freight Efficiency found reliability to be the number one criteria among fleets when selecting tire pressure systems since downtime negates the efficiency improvement.[20]
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Engines

Diesel engines are significantly more fuel efficient than gasoline engines and the vast majority of large, heavy-duty truck engines are designed to run on diesel fuel.  As a result of engine improvements and cleaner fuels, diesel engines today produce between 60 and 99 percent fewer emissions of sulfur dioxide, hydrocarbons, nitrogen oxides, and particulate matter when compared to earlier versions of these engines.

There are currently several different technologies available that can be used to increase engine efficiency and/or reduce emissions, including (but not limited to):[21]

  • Turbocharging – An exhaust-driven turbine drives a compressor to increase the air density going into the engine.
  • Electrification of engine accessories – Traditional belt- or gear-driven accessories can be converted to electric power.
  • Reduction of engine friction – Engine friction reduction has been pursued continuously by manufacturers through careful design and selection of advanced materials.
  • Improvement of diesel exhaust particulate matter (PM) control using a diesel particulate filter (DPF) with a catalyst coating – The use of a DPF can degrade the fuel efficiency of the engine owing to exhaust flow restriction and pressure buildup in the system or the need for additional fuel to maintain the operation of the DPF.  The use of catalyst coatings can help promote oxidation and reduce the need for additional fuel.
  • Improvement of diesel exhaust catalytic system efficiencies using selective catalytic reduction (SCR) – Control of nitrogen oxide (NOx) has been accomplished with cooled EGR and an SCR catalyst.
  • Improved driveline efficiency – New automated mechanical and automatic transmissions have been shown to improve fuel economy resulting in lower emissions.
  • Hybrid power trains – A hybrid vehicle combines at least two energy converters, such as internal combustion engines, electric drives, and hydraulic drives.

Federal regulations have played a key role in the advancement of engine technologies. More stringent engine emissions standards for heavy-duty trucks have been phased-in several times this decade, including in 2004 (pulled ahead to 2002), 2007, 2010 and 2014.  While these mandates progressively decreased allowable emissions from truck engines, average fuel economy for trucks declined, decreasing by 0.7 percent for combination trucks from 2001 to 2011.[22]

The 2014 GHG emissions and fuel consumption standards for medium- and heavy-duty vehicles focus on reversing this fuel economy trend and represent the beginning of the federal government’s efforts to mandate reductions in GHG emissions from trucks.
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Alternative Fuels

Alternative fuels are another option for reducing the consumption of petroleum products and emissions and generally include those fuels made from products other than petroleum.  Since medium and heavy-duty fleets are comprised largely of diesel engines, natural gas (in both its compressed [CNG] and liquefied [LNG] forms), biodiesel and hybrid engines are emerging alternative fuel options.  The typical driving range of a vehicle is a key factor in determining the most appropriate alternative fuel.  For example, CNG may be a suitable option for port drayage, city refuse haulers and local delivery trucks since these trucks tend to operate in closer proximity to a refueling station.  Diesel-electric hybrids may be best suited for local pick-up and delivery operations that utilize medium- to light-duty straight trucks.

CNG and LNG. Recent discoveries of large natural gas reserves across the U.S. have resulted in relatively low and stable natural gas prices. In April 2014, the average cost of diesel was $3.97 compared to an LNG diesel gallon equivalent (DGE) of $2.61 and a CNG DGE of $2.40.[23]  Therefore, vehicles that run on natural gas are an attractive option for certain operations seeking to reduce fuel costs.

Studies have also shown life-cycle GHG emissions reductions as high as 20 percent when LNG replaces diesel and as high as 30 percent when CNG replaces gasoline in fleet vehicles.[24]  Natural gas trucks are typically less fuel efficient, however.  The spark ignition engine used to power these trucks is roughly 15 percent less efficient than a diesel counterpart.[25]  Also, it should be noted that most natural gas is a fossil rather than a renewable fuel; although some natural gas can come from renewable sources, such as landfill and dairy gases. While these sources provide an opportunity for even greater reductions in GHG emissions, they are less abundant and can be more difficult to capture efficiently.

In contrast to the lower price of natural gas, the cost of a natural gas truck can range from $30,000 to $100,000 more than a comparable diesel truck, depending on the type of fuel system (CNG or LNG) and the size of the engine.[26]  Furthermore, few subsidies are available to offset this additional cost, leaving buyers dependent upon future fuel cost savings to offset the higher purchase price. Limited refueling sites, fuel venting and handling, and facility adaptation are additional issues that must be considered. Another factor is the uncertainty of energy markets. While the price of natural gas was relatively low in 2011 – 2013, some believe that costs will double by 2015 due to increasing demand.[27]   Such an increase in price could extend the payback period for CNG and LNG trucks.

Despite these challenges, several large motor carriers have purchased natural gas-fueled vehicles in recent years.[28]  Additionally, fleets that travel “point-to-point” or round-trip routes in operations such as waste collection and local delivery have been using natural gas for years.

Biodiesel and Renewable Diesel. Biodiesel is generally manufactured from vegetable oil or fats, with the majority produced from soybeans, and is available in its pure form (B100) as well as blended with petroleum-based diesel, typically at 2 (B2) to 20 percent (B20) ratios.  Use of this renewable fuel in its blended form can reduce diesel consumption and most tailpipe emissions without the need to modify the engine.  Some manufacturers, however, do not recommend using biodiesel blends above B5 in on-highway vehicles.[29]  Under certain conditions, high levels of fuel may accumulate in the engine lubricant which could affect engine performance.  Additionally, cold weather performance, fuel filter clogging, fuel quality, NOx emissions, and microbial growth are issues which must be considered when using biodiesel or biodiesel blends.[30]

Renewable diesel is an emerging product which is also manufactured from vegetable oil or fats.[31]  Similar to petroleum diesel, renewable diesel is refined by hydrotreating in a pure form or when blended with petroleum.  The finished fuel meets the ASTM specification for petroleum diesel which, unlike biodiesel, allows it to be transported through the existing petroleum pipeline network.

Biodiesel typically costs more at the pump and on an energy equivalent basis than diesel.  In April 2014, B20 cost $0.11 more and B99-100 cost $0.68 more per DGE than diesel.[32]  Similarly, renewable diesel costs more to produce than diesel fuel.[33]  While the future production levels and price of biodiesel and renewable diesel are uncertain, requirements mandating minimum volumes of these transportation fuels under the federal Renewable Fuel Standard continue to advance their use among motor fuel consumers.

truckstopDiesel-Electric Hybrids. Diesel-electric hybrid engines are used primarily in package and beverage delivery fleets.  These vehicles provide increased fuel efficiency and air quality benefits although they tend to be operated primarily in urban settings.  The cost of a hybrid heavy-duty truck can be as much as $60,000 more than a comparable diesel truck.[34]  Since these vehicles tend to be used in urban operations, overall mileage and fuel usage may be lower and require a longer payback period to offset the higher initial cost.

FedEx has been using diesel-electric hybrid trucks for urban deliveries for several years.  In 2008, the company reported a 42 percent gain in fuel economy compared with a traditional vehicle.[35]  UPS has also deployed nearly 400 hybrid electric vehicles that have improved fuel economy by 35 percent compared to the trucks that were replaced.[36]

Overall, the primary barriers to increased adoption of alternative fuels by the trucking industry are high vehicle acquisition cost and fuel availability.  And in the case of biodiesel where these barriers are not as prevalent, the higher fuel cost is a barrier.  These additional costs can be especially prohibitive for smaller fleets and owner-operators that may have limited access to the financial capital necessary to purchase more expensive equipment or fuel.  Furthermore, if additional on-site natural gas fueling infrastructure is necessary (which can range from $2 – $5 million), the initial expense can be prohibitive.[37]  As of April 2014, nearly half of the nation’s public and private LNG stations were located in California.[38]  Additionally, nearly half of the nation’s public and private fueling stations selling CNG or biodiesel were limited to five states, respectively.[39]  For truck fleets that have irregular routes, this limited fueling infrastructure is a major constraint to the advancement of alternative fuels.
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Cargo Management Systems

More efficient utilization of trailer space, whether through reduced empty trailer miles or strategic trailer loading, can further improve a fleet’s productivity. According to ATRI research, approximately 16 percent of for-hire fleet miles were empty in 2012.[40]

For a typical long-haul truck traveling 100,000 miles per year, this equates to 16,000 non-revenue producing miles annually while consuming more than 2,500 gallons of fuel. Assuming a diesel fuel price of $4.00 per gallon, non-revenue fuel costs would be $10,000 annually. As shown, matching freight demand to available capacity can be an important practice for saving fuel and lowering operating costs.

The Centre for Data and Analysis in Transportation studied the use of electronic vehicle management systems (EVMS) to improve trailer capacity utilization in Canada. Such systems are intended to match available freight capacity with demand for freight services from shippers.[41] The research found a 16 percent increase in the capacity utilization of trucks using EVMS.

In the U.S., the Federal Highway Administration’s (FHWA) Cross-Town Improvement Project (C-TIP) is developing methods to reduce the number of empty trailers moving between terminals in Kansas City by better coordinating cross-town truck traffic. C-TIP utilized several technologies to accomplish this, including real-time traffic monitoring, dynamic route guidance, chassis utilization tracking and wireless drayage updating. A pilot test of the wireless drayage updating system demonstrated a 13 percent reduction in empty trailer trips, saving a modest 121 gallons of fuel for the participating carriers over a 2 month period.[42]  According to FHWA, the cost of this type of service is expected to be low once it is provided by the private sector. A similar pilot test conducted in Chicago over four months in 2011 resulted in a 52 percent reduction in empty trailer movements.[43]  Combined, these systems have the potential not only to help carriers increase productivity through better asset management, but to reduce congestion levels in the surrounding areas.

Motor carriers also rely on a variety of private systems to match freight demand to truck availability. One fleet found improvements in data accuracy allowed them to further build out loads.[44]  Further, the emergence of load boards, which use the internet and/or cell phones, to match freight loads to truck availability are another practice which is reducing empty miles.

Transponders, including radio frequency identification devices (RFID) tags, in addition to cell phone can also be used to optimize cargo management. Transponders can be used to monitor and track the location of trailers, intermodal containers, and cargo in real-time. These devices also allow the identification of trucks in order to bypass weight stations, tolls plaza and at security check points.

Companies that operate their own fleet of trucks to support their primary business (i.e., private fleets) may be able to maximize their utilization of trailer space with compact packaging and innovative loading techniques. For example, Walmart found that the use of a two-step safety stool increased trailer fills by nearly 3 percent.[45]  In addition, a new load designer system in their grocery operations identifies unused space and more accurately designates pallet positions for optimal loading/off-loading.

Other examples of strategic loading include mixing items with high and low weights in order to balance space and weight limitations. Some carriers have been able to increase the number of pallets loaded onto a trailer using a technique called “pin-wheeling” (i.e. turning every other pallet by 90 degrees). Research found this technique resulted in an additional two pallets in a standard trailer.[46]  As shown by these examples, cargo management systems encompass a broad range of technologies and practices and continue to emerge as an important component of the sustainable practices being used by the trucking industry.
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Higher Productivity Vehicles

Another way of improving fuel efficiency and reducing emissions is through the use of higher productivity vehicles (HPVs). HPVs operate at heavier weights and/or longer lengths than traditional vehicle configurations. A number of studies have found HPVs to be more efficient at moving freight.

Among the three countries participating in the North American Free Trade Agreement (NAFTA), the United States has the lowest gross vehicle weight (GVW) limit.[47]  In the U.S., trucks are generally limited to an overall GVW limit of 80,000 pounds and typically use a single trailer that is 53 feet in length or less or two trailers of 28 feet or less.[48]  As shown in Figure 6, several states allow HPVs to operate on portions of the national highway system (NHS) without special permitting (but under certain restrictions). These states have been granted “grandfather rights” by the U.S. Congress which allow the operation of vehicles at weights and lengths greater than the current federal limits.

Figure 6.  Longer Combination Vehicle Routes on the National Highway System, 2009

Figure 6. Longer Combination Vehicle Routes on the National Highway System, 2009[49]

Examples of HPVs in use today include a six-axle tractor-semitrailer, a Rocky Mountain double, a triple trailer combination and a turnpike double as shown in Figure 7.

Figure 7.  Common Higher Productivity Vehicle Configurations

Figure 7. Common Higher Productivity Vehicle Configurations

Over several decades, states, motor carriers, shippers and other stakeholders have proposed changes to the federal truck size and weight limits and several states have sought exemptions from the federal limit in order to expand the HPV network. In late 2009, Congress approved a bill (H.R. 2112) that created a pilot program in Maine and Vermont allowing 108,000 to 120,000-pound six-axle trucks to operate on Interstate highways in Vermont and 100,000-pound six-axle trucks on Interstate highways in Maine. The benefits of the program were illustrated by Champlain Oil Company, which saved 43,400 gallons of diesel fuel and traveled 320,000 fewer miles during the one-year program.[50]  While the pilot program expired in December 2010, legislation which exempts the Maine and Vermont Interstate highways from federal vehicle weight limits for a 20-year period was signed into law in November 2011.[51]

In the ATRI report Energy and Emissions Impacts of Operating Higher Productivity Vehicles, Update 2008, researchers quantified the energy and emissions impacts that can result from operating trucks at various weights and configurations.[52]  Six common vehicle configurations were modeled through this research over a typical route to estimate fuel consumption and emissions. Increases in fuel efficiency were observed for nearly every HPV configuration evaluated. As an example, vehicles operating at 120,000 pounds GVW had fuel efficiency increases that ranged from 15 to 31 percent while increases of 33 percent were observed for vehicles operating at 140,000 pounds GVW.

In Canada, the Ontario Ministry of Transportation initiated a one-year pilot program to monitor and analyze HPV operations by allowing a limited number of HPVs (up to 100) on designated Ontario highways.[53]  The program reported that each HPV used approximately one-third less fuel than the two tractor-trailers it replaced. The authors also estimated that an expansion of this program could reduce fuel consumption by more than 18 million gallons annually.

A Canadian Trucking Alliance report documents the potential benefits of HPV operations in the provinces of Quebec, Alberta, Manitoba and Saskatchewan.[54]  The focus of this research was the turnpike double (a Class 7 or 8 tractor pulling two semitrailers) and researchers collected actual fuel consumption data from carriers. The findings were consistent with previous research that found HPVs can yield fuel consumption savings of 30 percent or more.

Furthermore, in a study commissioned by Alberta Infrastructure, researchers found that HPVs were significantly more efficient than conventional tractor-trailer combinations.[55]  The use of HPVs (at a GVW of 62,500 kg and a length of 37 m or approximately 137,800 lbs and 121 ft) within the Alberta province has saved shippers approximately C$40 million annually and reduced traffic levels by nearly 44 percent.[56]  Across the study network, the annual diesel fuel consumed by trucks has been reduced by 32 percent through the use of HPVs, which equates to an annual fuel savings of approximately 4 million gallons.[57]

Finally, in the United States, FHWA examined potential changes to the federal truck size and weight limits through its 2000 Comprehensive Truck Size and Weight Study.[58]  The study outlines several scenarios where potential changes in truck size and weight could be made; the outcome of the four HPV scenarios were decreases in total truck vehicle miles traveled (VMT) ranging from 10.6 to 23.2 percent and decreases in energy costs of 6.2 to 13.8 percent.

Changes in federal law are the key to the increased deployment of HPVs and the most recent surface transportation authorization bill, Moving Ahead for Progress in the 21st Century (MAP 21), includes provisions for a two-year study on the impacts of increased truck sizes and weights. The study, which is expected to be released in late 2014, will examine the potential effects on highway safety and infrastructure as well as violation rates and enforcement costs across the U.S. In addition to two control configurations (a 5-axle tractor-trailer and a tractor plus two 28 or 28.5-foot trailers), four alternative configurations will be evaluated:[59]

  • 6-axle tractor-trailer
  • tractor plus two 33-foot trailers (6-axle)
  • tractor plus three 28 or 28.5-foot trailers (7-axles)
  • tractor plus three 28 or 28.5-foot trailers (9 or 10-axles)

Since some states currently allow twin 33-foot trailers, a number of motor carriers have already evaluated their performance. Based on data supplied by FedEx, ABF System, Con-way, Estes Express, Old Dominion Freight Line, UPS and YRC Worldwide, the industry could absorb up to 18 percent of future freight growth without any change in gross vehicle weight or additional miles traveled if the standard for twin trailers was increased to 33-feet.[60]
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[5] Improved Aerodynamics: A Glance at Clean Freight Strategies. Environmental Protection Agency, SmartWay Transport Partnership. Available online: http://www.epa.gov/smartway/forpartners/documents/trucks/techsheets-truck/EPA-420-F00-036.pdf

[6] EPA and NHTSA Adopt First-ever Program to Reduce Greenhouse Gas Emissions and Improve Fuel Efficiency of Medium- and Heavy-duty Vehicles. Environmental Protection Agency. (2011) Available online: http://www.epa.gov/oms/climate/documents/420f11031.pdf

[7] Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles, National Research Council, Transportation Research Board. (2010) pp 133-138. http://www.nap.edu/catalog.php?record_id=12845

[8] Truck Manufacturers Association. (2007). Test, Evaluation and Demonstration of Practical Devices/Systems to Reduce Aerodynamic Drag of Tractor/Semitrailer Combination Unit Trucks. National Energy Technology Laboratory. Available online: http://www.kronosenergysolutions.com/pdfs/DOE-TMAtests.pdf

[9] Ibid.

[10] Sharpe, B., and M. Roeth, Costs and Adoption Rates of Fuel-Saving Technologies for Trailers in the North American On-Road Freight Sector, The International Council on Clean Transportation http://nacfe.org/wp-content/uploads/2014/03/ICCT_trailer-tech-costs_20140218.pdf (2014).

[11] Ibid.

[12] National Research Council, Transportation Research Board. Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two, p. 2-6 (First Report, 2014). Available online: http://www.nap.edu/catalog.php?record_id=18736

[13] Bennet, S. Low Rolling Resistance Tires Gain Traction with Carriers Seeking to Save Fuel, Money. Transport Topics. 6/20/2011.

[14] National Research Council, Transportation Research Board, Ibid, p. 6-7.

[15] Downing, K. and S. Matthews. (2010). Improving Truck Efficiency and Reducing Idling. State of Oregon Department of Environmental Quality. Available online: http://www.deq.state.or.us/aq/committees/docs/truck/improveEfficiencyReport.pdf.

[16] National Research Council, Transportation Research Board, Ibid.

[17] Ibid.

[18] Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles, National Research Council, Transportation Research Board, p. 134 (2010). http://www.nap.edu/catalog.php?record_id=12845

[19] U.S. DOT, FMCSA, Advanced Sensors and Applications: Commercial Motor Vehicle Tire Pressure Monitoring and Maintenance, (February 2014). Available online: http://ntl.bts.gov/lib/51000/51800/51837/13-021-Adv_Sensors__Applications_CMV_Tire_Pressure_Monitoring___Maintenance-Report.pdf

[20] North American Council for Freight Efficiency, Tire Pressure Systems (August 15, 2013). Available online: http://nacfe.org/wp-content/uploads/2014/01/TPS-Detailed-Confidence-Report1.pdf

[21] National Research Council, Transportation Research Board. Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two, p. 2-6 (First Report, 2014). Available online: http://www.nap.edu/catalog.php?record_id=18736

[22] Transportation Energy Data Book: Edition 32 – 2013. U.S. Department of Energy. Available online: http://cta.ornl.gov/data/index.shtml.

[23] U.S. Department of Energy. Clean Cities Alternative Fuel Price Report. Available online: http://www.afdc.energy.gov/uploads/publication/alternative_fuel_price_report_april_2014.pdf.

[24] California Air Resource Board, Carbon Intensity Look-Up Tables. 1/6/2011

[25] National Research Council, Transportation Research Board. Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two, p. 5-2 (First Report, 2014). Available online: http://www.nap.edu/catalog.php?record_id=18736.

[26] ACT Research, The Future of Natural Gas Engines in Heavy Duty Trucks: The Diesel of Tomorrow (August 10, 2012).Available online: http://www.actresearch.net/wp-content/uploads/2013/04/ACT_NGP.pdf.

[27]Chazan, Guy. Shell warns on US Natural Gas Bounce. The Financial Times. Accessed 5/24/2012 at http://www.ft.com/intl/cms/s/0/e34957ac-9f65-11e1-a255-00144feabdc0.html#axzz1vtPesmDF.

[28] FleetOwner.com – Running Green, http://fleetowner.com/running-green.

[29] National Biodiesel Board, OEM Statement Summary Chart, Available online: http://www.biodiesel.org/using-biodiesel/oem-information/oem-statement-summary-chart.

[30] Biodiesel Handling and Use Guide. National Renewable Energy Laboratory. (2009). Available online: http://www.nrel.gov/vehiclesandfuels/npbf/pdfs/43672.pdf.

[31] Alternative Fuels Data Center, Hydrogenation-Derived Renewable Diesel, Available online: http://www.afdc.energy.gov/fuels/emerging_green.html

[32] U.S. Department of Energy. Clean Cities Alternative Fuel Price Report. Available online: http://www.afdc.energy.gov/uploads/publication/alternative_fuel_price_report_april_2014.pdf.

[33] Milbrandt, A., C. Kinchin, and R. McCormick, National Renewable Energy Laboratory, The Feasibility of Producing and Using Biomass-Based Diesel and Jet Fuels in the United States (December 2013).

[34] California Air Resources Board, Fiscal Year 2014-15 Funding Plan for the Air Quality Improvement Program and Low Carbon Transportation Greenhouse Gas Reduction Fund Investment (May 23, 2014). Hybrid Truck and Bus Voucher Incentive Project. Available online: www.californiahvip.org.

[35] FedEx. (2008). FedEx Hybrid-Electric Fleet Surpasses Two-Million-Mile Mark. FedEx News. Available online: http://news.van.fedex.com/2MMiles

[36] UPS Press Release. Saving Fuel: Alternative Fuels Drive UPS to Innovative Solutions. Available online: http://pressroom.ups.com/Fact+Sheets/Saving+Fuel%3A+Alternative+Fuels+Drive+UPS+to+Innovative+Solutions.

[37] “When to Use LNG vs. CNG for Trucking” webinar. Available online: www.cleanenergyfuels.com.

[38] Alternative Fueling Station Total Counts by State and Fuel Type. U.S. Department of Energy. Available online: http://www.afdc.energy.gov/afdc/fuels/stations_counts.html.

[39] Ibid.

[40] Fender, K. J. and Pierce, D., An Analysis of the Operational Costs of Trucking: A 2013 Update. American Transportation Research Institute (2013).

[41] Barla, P., et al., Information Technology and Efficiency in Trucking, Centre for Data and Analysis in Transportation, Québec, Canada (2010).

[42] Schiller, R., C-TIP Evaluation: Results and Lessons Learned, Talking Freight Presentation (1/18/2012).

[43] Ibid.

[44] Walmart, 2014 Global Responsibility Report, http://cdn.corporate.walmart.com/db/e1/b551a9db42fd99ea24141f76065f/2014-global-responsibility-report.pdf

[45] Ibid.

[46] Santalucia, A., et al. Beyond SmartWay: New Opportunities for Fuel Savings and Emission Reductions in the Trucking Sector. ICF International, Transportation Research Board 2011 Annual Meeting.

[47] Transportation Research Board, Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles, Special Report 267, Washington, D.C., http://onlinepubs.trb.org/onlinepubs/sr/sr267.pdf (2002). (The maximum legal weight of a six-axle truck in Mexico is approximately 106,700 pounds and in Canada is 95,700 to 116,600 pounds depending on the province and axle spacing.)

[48] The Federal government began regulating truck size and weight limits in 1956 with the construction of the Interstate Highway System. Congress established a maximum gross vehicle weight limit of 73,280 pounds along with maximum weights of 18,000 pounds on single axles and 32,000 pounds on tandem axles for vehicles operating on the Interstate system. The Federal-Aid Highway Act Amendments of 1974 increased the maximum GVW to 80,000 pounds and to 20,000 pounds on single axles and 34,000 pounds on tandem axles. This increase was due in part to the rising fuel costs at the time. The Surface Transportation Assistance Act of 1982 expanded the federal authority, essentially overriding several more restrictive “barrier” states located along the Mississippi that had not adopted the previous size and weight limit increase. The most recent legislation related to truck size and weight limits was in the Intermodal Surface Transportation Efficiency Act of 1991, which froze the limits to those established in 1974.

[49] United State Department of Transportation, Federal Highway Administration, Freight Facts and Figures, 2010.

[50] Heavy Duty Trucking, Bill Would Make Larger Truck Pilot Program Permanent, http://www.truckinginfo.com/news/news-print.asp?news_id=72795 (1/26/2011).

[51] H.R 2112 was signed by President Obama on November 18, 2011 and contained the following:

“Sec. 125. Section 127(a)(11) of title 23, United States Code, is amended to read as follows:

(11)(A) With respect to all portions of the Interstate Highway System in the State of Maine, laws (including regulations) of that State concerning vehicle weight limitations applicable to other State highways shall be applicable in lieu of the requirements under this subsection through December 31, 2031.

(B) With respect to all portions of the Interstate Highway System in the State of Vermont, laws (including regulations) of that State concerning vehicle weight limitations applicable to other State highways shall be applicable in lieu of the requirements under this subsection through December 31, 2031.

[52] Tunnell, M.A., Energy and Emissions Impacts of Operating Higher Productivity Vehicles, Update 2008, American Transportation Research Institute (2008).

[53] Ontario Ministry of Transportation, Ontario LCV Pilot Program Questions and Answers, http://www.mto.gov.on.ca/english/trucks/lcv/questions-and-answers.shtml (2010).

[54] Canadian Trucking Alliance, Evaluating Reductions in Greenhouse Gas Emissions Through the Use of Turnpike Double Truck Combinations and Defining Best Practices for Energy Efficiency, L-P Tardif & Associates Inc. in association with Ray Barton Associates Ltd. (2006).

[55] Woodrooffe, J. and Ash, L., Economic Efficiency of Long Combination Transport Vehicles in Alberta, http://www.transportation.alberta.ca/Content/docType61/production/LCVEconomicEfficiencyReport.pdf Woodrooffe and Associates (2001).

[56] Compared to traffic levels if those vehicle movements had occurred in non-HPV trucks.

[57] Woodroofe, et al. Ibid.

[58] U.S. Department of Transportation, Comprehensive Truck Size and Weight Study (2000).

[59] U.S. Department of Transportation, Presentation: USDOT Comprehensive Truck Size and Weight Limits Study, MAP-21 §32801, Public Input Meeting #3, May 6, 2014 http://ops.fhwa.dot.gov/Freight/sw/map21tswstudy/outreach/session050614/presentation/public_input_mtg3.pdf.

[60] Vice, A., FedEx presses Congress for 33-ft. twin trailers, Fleet Owner Magazine, http://fleetowner.com/fleet-management/fedex-presses-congress-33-ft-twin-trailers (2/27/2014).

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