Today’s market is awash in alternative -fuel options­ — from biodiesel to natural gas to electricity to propane autogas. While each has clear advantages for use in medium-duty (Class 4-7) trucks, they also have disadvantages. The key to getting the right menu of fuel sources is to understand their advantages and disadvantages, weigh them, and make a decision based on a fleet’s needs. The following is an overview of the leading alt-fuel technologies in the medium-duty market spotlighting each option’s benefits, drawbacks, and potential future as fleet fuel sources. 

Biodiesel is a clean-burning alternative renewable fuel produced from vegetable oils (such as soybeans), animal fats, and yellow grease (recycled cooking oil from restaurants). The term “biodiesel” technically refers to the pure fuel (100-percent biodiesel or B-100) before blending with diesel fuel. Biodiesel “blends” are labeled in terms of percent biodiesel. For example, B-5 is a blend of 5-percent biodiesel and 95-percent diesel. 

Reduced emissions. According to the U.S. Environmental Protection Agency (EPA), B-20 biodiesel blend cuts unburned hydrocarbons by 20 percent, carbon monoxide by 12 percent, and particulate matter by 12 percent, compared to conventional diesel. 

Low initial investment to “go green.” Biodiesel operates in conventional diesel engines with few, if any, modifications and is distributed using today’s infrastructure, enabling fleets to keep spare parts’ inventories, leverage central fueling stations, and utilize skilled diesel mechanics, which keeps costs low.

Growing original equipment manufacturer (OEM) acceptance. All major automakers and engine manufacturers in the U.S. accept the use of at least B-5.

“Now more than 60 percent of those companies also support B-20 or higher blends, making it easier for fleets to use biodiesel blends in their vehicles with confidence,” said Jennifer Weaver, OEM outreach and education specialist for the National Biodiesel Board (NBB).

Fuel infrastructure and cost. Currently, there are more than 3,600 retail and distributor outlets for biodiesel in the U.S. Biodiesel distributors also deliver fuel to fleets’ own central fueling tanks nationwide. The federal biodiesel tax credit and numerous state incentives help to bring the cost of biodiesel in line with petroleum diesel. 

“However, in order to guarantee the most efficient, widespread, and cost-effective distribution of biodiesel over the long term, more biodiesel will need to be transported via pipeline,” Weaver said. “There is already one U.S. pipeline actively transporting biodiesel blends, and substantial research is currently underway with the pipeline and petroleum industries to enable greater biodiesel distribution via pipeline in the future.”    

Fuel quality. Biodiesel that does not meet strict quality standards can diminish engine performance, clog filters and injectors, and cause numerous other costly repairs. While this is a concern at the moment, high-standard biodiesel is being produced.

“Today, biodiesel production is held to extremely high-quality standards as dictated by a thorough and constantly improving set of American Society of Testing & Materials (ASTM) specifications for biodiesel,” Weaver explained. “Those standards include ASTM D6751 for pure biodiesel, ASTM D975 for blends up to 5-percent biodiesel, and ASTM D7467 for blends between 6 and 20 percent. Biodiesel fuel quality is further ensured by the industry’s robust quality control program, BQ-9000.”

Cold weather operability. “The performance of biodiesel in cold conditions is markedly worse than that of petroleum diesel,” said Anthony Radich, U.S. Department of Energy analyst. In his study Biodiesel Performance, Costs, and Use, Radich noted that the temperature at which wax crystals can form and potentially clog fuel lines and filters with biodiesel is higher than that for petroleum diesel. 

On the upside, fuel suppliers can produce biodiesel with additives that enable it to perform in extremly cold conditions.

In July 2010, the U.S. EPA implemented the Renewable Fuels Standard 2, calling for increased volumes of biodiesel to be used in the U.S. marketplace through at least 2022. The biodiesel production requirement for 2011 is 800 million gallons, ramping up to as much as 5 billion gallons by 2022. “With more biodiesel available in the marketplace and ever-increasing support for biodiesel by the original equipment manufacturer (OEM) community, the future for fleet use of this advanced biofuel looks very bright,” Weaver explained.

Natural gas vehicles (NGVs) use internal combustion engines that are very similar to those that run on gasoline or diesel. There are two types of NGV systems: dedicated and bi-fuel. Dedicated systems are designed to run exclusively on natural gas; bi-fuel can run on natural gas or conventional fuel (diesel or gasoline) but not both at the same time.
Light-duty sedans, pickups, and some smaller medium-duty trucks use either dedicated or bi-fuel systems, while most medium- and heavy-duty engines run dedicated systems only.

Natural gas may be stored onboard in one of two ways, either as compressed natural gas (CNG) or liquefied natural gas (LNG). LNG is currently used in less than 5 percent of NGVs with nearly all used by heavy-duty trucking and some transit bus operations because its density allows for a smaller fuel system footprint. CNG is far more prevalent in light-duty and medium-duty work trucks.

Factory-built NGVs for delivery fleets, public works, and other larger work truck applications (Class 6 and larger) are available from many of the major truck manufacturers, including Freightliner, Peterbilt, Kenworth, and International. Conversions are available on Class 5-7 Workhorse, Freightliner Custom Chassis Corp (FCCC), and Isuzu trucks ordered with gasoline engines.

Environmental benefits. According to Natural Gas Vehicles for America (NGVAmerica), NGVs produce up to 95-percent less overall toxins compared to gasoline and diesel vehicles, and produce between 20- and 30-percent less greenhouse gas emissions.

North American fuel source. Since nearly 98 percent of all natural gas used in the U.S. comes from North America, proponents argue that increased use, especially in the transportation sector, which currently relies heavily on imported oil, is a viable path for the United States to achieve greater energy independence now and for the foreseeable future.
Comparatively low fuel costs. In the most recent Clean Cities Alternative-Fuel Price Report (, CNG offers a savings of $1.74 per equivalent gallon of diesel and $1.82 per equivalent gallon of gasoline.  

“Current national fuel prices provide a compelling case for converting, and, depending on the fleet application, provide a payback period of two to four years,” said Jonathan Culp, manager of strategic alliances for PHH Arval.  

NGV Premium. The incremental cost on OEM-equipped and after-market conversion natural gas vehicles varies widely based on the amount of fuel storage installed, but may range from $20,000 to as much $50,000.

While there have been substantial federal and state tax incentives and/or grants that lower NGV purchase premiums in the past, the federal credit for purchasing NGV expired at the end of 2010, but there still are state-level incentives.

Infrastructure. Despite fuel cost advantages, this is a primary constraint impeding widespread fleet adoption of natural gas, even in high-mileage applications. Currently, there are about 1,000 compressed natural gas (CNG) fueling locations in the U.S., but only 50 percent are open to the public. A listing of public CNG refueling stations is available at:

Natural gas has some clear advantages, but the lack of a natural gas infrastructure is a big hurdle to its widespread implementation.

“While some states, such as California and Utah, have a more well developed natural gas refueling infrastructure, we need to spur the investment needed to increase the pace of construction,” said Kathryn Clay, executive director of the Drive Natural Gas Initiative. “The [recent] announcement by Chesapeake Energy of its partnership with Clean Energy Fuel’s Corp will bring about another 150 liquefied natural gas (LNG) stations to our nation’s interstates. While this is an important step, more needs to be done.”

Clay added that federal tax incentives could help, as could decisions by local public utility commissions to encourage the development of NGV refueling stations.

Propane autogas, also known as liquefied petroleum gas (LPG), is used as a fuel in internal combustion engines in light-, medium-, and heavy-duty vehicles. Propane is produced from both natural gas processing and crude oil refining, in roughly equal amounts from each source. Proponents point to the fuel’s potential to wean America off foreign oil, as 97 percent of propane consumed in the U.S. is produced in North America.

Widespread use. Propane autogas is the third most common vehicle fuel in the United States, used in bus, taxi, shuttle, and light- and medium-duty truck fleets, according Steve Wayne, chief technology officer, Propane Education & Research Council (PERC). He attributes the expansion of propane to a rapidly growing maintenance and refueling infrastructure, in addition to increased availability of propane-autogas-fueled vehicles. 

Fuel cost savings. According to a recent Clean Cities Alternative Fuel Price Report, propane autogas offers 86-cents-per-gallon savings compared to diesel. 

Reduced emissions. “Propane autogas-fueled fleet vehicles emit 12-percent less carbon dioxide, about 20-percent less nitrogen oxide, and up to 60-percent less carbon monoxide than gasoline-fueled vehicles, which provide a sustainable solution for fleets looking to reduce emissions and fuel costs,” Wayne said.

Conversion Cost. Trucks equipped with liquid propane autogas injection systems have an initial purchase price between $4,000 to $12,000 more than conventional gasoline or diesel trucks. 

“The conversion cost can be offset by the lower cost of propane autogas (compared to diesel and gasoline), reduced maintenance costs over the life of a vehicle, and extended engine life,” Wayne explained. “Propane autogas burns cleaner in engines than gasoline and diesel, resulting in reduced maintenance costs and longer engine life, which helps curb costs. 

Limited availability of propane-autogas-fueled vehicle platforms. Wayne said the industry has been aggressively investing in development to rollout a wider range of propane-autogas vehicles for fleets.

“In the past two years, more than a dozen new on-road platforms fueled by propane autogas have been developed with funding from PERC, and more vehicle platforms are currently being developed by ROUSH CleanTech, CleanFuel USA, and Freightliner Custom Cab and Chassis,” Wayne said.

Limited Fueling Infrastructure. “The propane industry has worked with fleets to establish a refueling infrastructure that works best for fleets’ needs,” Wayne said. “Onsite refueling dispensers are available for centralized fleets, while thousands of offsite refueling stations across the U.S. make propane autogas readily available.” 

To find the nearest propane fueling station, go to:  
For more information for centrally fueled fleets, visit:

While not a common part of a medium-duty fleet’s fuel menu, there are examples of market segments that are showing the relevance and successful implementation of propane-autogas-fueled vehicles. 

“The acceptance of school buses, airport, ground transportation, and delivery vehicles is positive proof that propane-autogas-fueled fleet vehicles make sense not only today, but also in the future, as pressure for fleet managers to run sustainable and cost-effective operations increases,” Wayne said. “PERC anticipates growth in this marketplace with new engine technologies and products, and is positioned to continue to support growth in this market through research and development, safety, and training programs.”

Also known as plug-in electric vehicles (PEVs) and battery-electric vehicles (BEVs), all-electric medium-duty trucks are propelled entirely by electricity from the utility grid, with a range of 80 to100 miles or more on battery power. 
OEMs such as Navistar (, Smith Electric (, ZeroTruck (, and Freightliner Customer Chassis Corp. ( offer all-electric trucks with gross vehicle weight ratings (GVWRs) of 12,000-lbs. to 29,500-lbs., top speeds up to 65 mph, and ranges up to 100 miles on a full charge.

Zero tailpipe emissions. Since BEVs do not burn liquid or gaseous fossil fuels at any time, they produce zero tailpipe emissions. 

Lower fuel and operational costs. The biggest advantage for PEVs and BEVs from a fleet perspective is the operating costs for electric vehicles are substantially lower than diesel trucks. “The cost-per-mile for BEVs may be a third of the cost-per-mile for diesel trucks of the same weight class, including maintenance costs,” said Dave Hurst, senior analyst, Pike Research.

High initial cost. The upfront cost of medium-duty electric trucks is about double that of diesel, and fleets are typically incurring additional costs for the recharging infrastructure, including potentially trenching for the charging equipment power line and adding new electric service. “These costs may not be included in a cost-per-mile calculation, but are definitely considered when calculating the return on investment” Hurst noted. 

To narrow the price gap, the Recovery Act established tax credits for purchasing electric vehicles ($2,500-$7,500 per vehicle, depending on the battery capacity) and conversion kits to retrofit conventionally powered vehicles with electric vehicle capability ($4,000 per vehicle, maximum). For details on the federal tax incentive go to:

Some states are also offering as much as $5,000, in addition to federal incentives, in tax credits for electric vehicles. For more information on these state tax incentives, visit

Limited applications. Since the existing range for all-electric medium-duty trucks is approximately 100 miles, there is a small niche in which these trucks can feasibly operate — most prominently the urban-delivery market. 

Limited charging infrastructure. All-electric medium-duty trucks currently work best for fleets that have return-to-base operations, where the trucks can charge overnight and then deploy on their routes the next day, without the need to recharge while away from “home.” 

So, what’s holding back BEV growth in the medium-duty market is the ability to charge away from home base, to reduce “range anxiety” for drivers, and extend routes beyond existing battery range limits. To overcome this challenge, federal stimulus money is being used to subsidize developing residential and commercial “quick charge” EV charging stations in select urban markets. 

Genevieve Cullen, vice president, Electric Drive Transportation Association (EDTA), expects to see battery electric vehicle (BEV) fleets growing over the next five to 10 years. “Announcements of substantial purchase plans by some of the largest fleets — General Electric, FedEx Express, and UPS — are indicators of the market’s growing interest,” she said. “Market share will grow faster as costs come down over the next few years as manufacturers achieve economies of scale.”

Medium-duty hybrids use a combination of diesel and electricity. In slower (below 30 miles per hour) stop-and-go traffic, the hybrid system acts primarily as an electric motor, drawing power from the battery pack, and automatically switches between electricity and diesel, as needed. In steady driving conditions above 30 miles per hour, the hybrid truck is powered by the diesel engine.

Factory-built hybrid trucks are available from Kenworth (T270 Class 6 and T370 Class 7 Hybrids), Peterbilt (330 Hybrid), and International (Durastar Hybrid). There are also several aftermarket hybrid conversion systems compatible with most medium-duty trucks.

Fuel cost savings. According to Hurst at Pike Research, the operational cost (including fuel and maintenance) of medium-duty hybrids is approximately 25-percent lower than conventional diesel-powered trucks. 

Extended range compared to all-electric vehicles. “If it’s an application where the vehicle needs to be in a heavier class (Class 5 and up), needs an energy-hungry refrigeration unit or other equipment, will need to be used for multiple shifts (so no downtime to recharge), or has a full load at the end of its route, then a hybrid may be a better match,” Hurst said.

High conversion cost.  Hybridization is expensive — as much as $20,000-$30,000 or more — so it’s a good idea to do extensive route analysis before undertaking a hybridization project, advised Jonathan Culp, manager of strategic alliances, PHH Arval, a full-service fleet management company based in Sparks, Md. 

“Begin by matching the drive cycle and route to a specific conversion spec to ensure that you will be able to achieve the goals of the project,” he said. “For example, I would not advise a client to hybridize a long-haul vehicle. Rather, I would recommend doing so to a vehicle that makes constant starts-and-stops and has a known delivery route.”

Both BEV and hybrid medium-duty trucks should both see strong growth and be on similar trajectories to some degree, predicted Hurst of Pike Research. 

“The difference between them is that the hybrid truck market has a 10-year head start on the BEV truck market at the moment,” he explained. “So, while we anticipate that hybrid medium-duty trucks will reach sales of almost 13,000 vehicles per year by 2017, during that same year, BEV trucks will likely sell about 3,000. The main reason for the differences will be the costs and the duty cycle of the two vehicles will appeal to different fleets for different reasons.”

The Bottom Line
So, which green energy source is the best? The short answer, according to the experts, is all of them, but for different reasons.

“Ten years from now, fleets will most likely have some of each of these technologies, along with emerging technologies such as plug-in hybrids, hydrogen fuel cells, and perhaps, even near-field charging,” said Culp of PHH Arval. “This is not a VHS versus Betamax issue. All of these technologies are going to be important in helping to reduce our petroleum dependence, and each will provide a positive return on the investment given the right niche and fleet application. I would advise companies to stay current with emerging trends and build partnerships with other fleets to find out what is working for them.”