Fuel economy 101

Trucking is an industry with already thin profit margins, and especially in an economic downturn, the effects of escalating and volatile fuel costs are a major cause of concern for even the most conscientious fleet operator. Fuel continues to be the second largest expense for trucking companies, just behind labor costs, therefore, increasing fuel efficiency and minimizing fuel consumption should be a major goal of any truck fleet operator.

While the price of fuel may be out of the industry's control, there are many ways fleet managers can manage fuel consumption. The first step in reducing fuel consumption, according to the American Trucking Assns. (ATA), is reducing speed. A truck traveling at 75 mph consumes 27% more fuel than one going 65 mph; so limiting truck speed to 65 mph would save 2.8 billion gals. of diesel fuel over a decade. Consequently, the trucking association has recommended enacting a national speed limit not to exceed 65 mph and governing speeds on trucks manufactured after 1992 at no more than 65 mph.

Idling is another huge fuel guzzler. ATA is also pursuing a federal solution that reduces nondiscretionary idling through highway infrastructure improvements and reduces discretionary idling through incentives for new technology. Nondiscretionary idling is when the truck is stuck in congested traffic. Discretionary idling is when drivers idle their engines during rest periods to provide heat or air conditioning for the sleeper compartment, keep the engine warm during cold weather, and provide electrical power for in-cab appliances. These types of idling consume an estimated 1.1 billion gals. of diesel fuel every year.

One of the best ways to run lean is for shippers and carriers to join the U.S. Environmental Protection Agency (EPA) SmartWay Transport Partnership Program. SmartWay is an innovative collaboration between EPA and the freight industry to increase energy efficiency and significantly reduce greenhouse gases and air pollution. The SmartWay program includes representatives across the freight industry — shippers, truckers, rail carriers, even dealer service centers and truck stops.

ATA also advocates initiatives to improve highway infrastructure and reduce congestion. It has recommended a 20-year program, focused initially on fixing critical bottlenecks, and in the longer term creating truck-only corridors which would permit carriers to further increase the use of more productive vehicles. Research shows that increased volumes of freight can be moved with less fuel and fewer emissions by using a smaller number of large trucks rather than a larger number of small trucks. Permitting truck combinations to be more productive will help reduce the number of trucks needed on the road and reduce fuel consumption.

ATA also supports setting technologically feasible national fuel economy standards for medium- and heavy-duty trucks that reduce fuel consumption, if they do not compromise the performance of the vehicles.

Aside from national policy issues, there are steps trucking operators can take now to improve average fuel consumption through a range of engineering innovations, driving techniques, investment in the latest engines on the market, aerodynamic features, and lightweight design options.

THE DRIVER FACTOR

Drivers are not only the number-one expense of trucking companies; they are the major determining factor when attempting to control a fleet's number-two expense: fuel. According to ATA's Technology and Maintenance Council (TMC), the most skilled drivers can produce as much as 35% better mpg than less-skilled truck operators. Driver education, accordingly, is one of the most important tools in the large truck fuel economy arsenal. Even the most experienced truck drivers can improve their skills and enhance driving performance through training programs.

A driver training program that improves fuel economy 5% could save over $1,200 in fuel costs per vehicle each year, according to EPA. The agency cites several studies that conclude driver training can have a dramatic impact on a fleet's fuel performance:

• A Canadian study estimates that many fleets could achieve a 10% fuel economy improvement through driver training and monitoring. For a typical combination truck, a 10% saving is the equivalent of nearly $2,500 a year.

• A study for the European Commission estimates that incorporating an annual one-day driver training course into a trucking operation will improve truck fuel efficiency by 5%.

• Two trucking fleets in Canada documented the impact of driver training and found fuel efficiency improvements of 18 and 20%.

According to EPA, other factors that burn fuel include driving 65 mph instead of 55, which can use up to 20% more fuel; idling an engine, which burns almost 1 gal. of fuel per hour; and driving with too-high an engine rpm can waste several gallons of fuel each hour. Other common habits that reduce fuel economy are frequent or improper shifting, too-rapid acceleration, too-frequent stops and starts from failing to anticipate traffic flow, and taking circuitous routes. Driver training may generate even larger efficiency gains for vehicles in urban service where shifting practices have more influence on fuel economy.

Well-trained drivers can reduce fuel consumption by applying a number of simple techniques including:

• Driving at the lowest engine speed possible.

• Using cruise control where appropriate.

• Braking and accelerating smoothly and gradually.

• Using progressive shifting techniques (upshift at the lowest rpm possible).

• Block shifting (for example, go from 2nd gear to 5th gear).

• Coasting wherever possible.

• Limiting unnecessary truck idling.

• Starting out in a gear that doesn't require the use of the throttle when releasing the clutch.

• Limiting unnecessary shifting.

• Limiting the use of cab accessories to reduce parasitic energy losses.

Electronic engine monitors can also be used to review drivers' operating patterns and benchmark individual performance over time. Using these benchmarks, carriers can provide incentives to drivers who reduce fuel consumption. Successful incentive programs will pay bonuses regularly and frequently, set realistic goals, and are simple to administer, according to SmartWay. Fleets can obtain assistance in administrating such programs through national and local trucking organizations. And carriers can utilize the expertise of equipment suppliers and for-profit training organizations to teach drivers fuel-saving techniques.

For a typical long-haul truck, the initial cost of training and the purchase of related equipment such as electronic engine monitors and recorders could be recouped from fuel cost savings within two years, according to EPA. Carriers can realize even greater fuel and maintenance savings using technologies that limit truck idling, such as auxiliary power units and highway speed limiters.

REDUCING HIGHWAY SPEED

A typical combination truck spends 65% or more of its operating time at highway speeds. Line-haul trucks spend even more time on highways. The impact of speed on fuel economy depends upon many factors including vehicle aerodynamics, engine speed and operating conditions. As a general rule of thumb, increasing speed by 1 mph reduces fuel economy by about 0.1 mpg. For a truck with poor aerodynamics, the fuel penalty can double. Increased speed also leads to higher maintenance costs by increasing wear on the engine, tires and brakes.

A long-haul truck with 90% highway operation that reduces its top speed from 70 to 65 mph could cut its annual fuel bill by $1,450 or more, according to EPA. Reducing the maximum speed to 60 mph could save an additional $1,850, bringing the estimated annual savings to $3,300 per truck per year. As fuel prices increase, the economic benefits are more pronounced.

The most successful speed management policies combine technologies such as speed limiting devices and electronic engine controls with driver training and incentive programs to encourage drivers to maintain speed limits. When purchasing new vehicles, SmartWay recommends considering spec'ing equipment designed to optimize truck performance at lower maximum speeds.

Reducing speed can also reduce maintenance costs and reduce the frequency of downtime for shop work. The time between engine overhauls, for example, is directly related to fuel use. Holding maximum speeds at 60 mph rather than 70 mph reduces engine wear and extends time between engine rebuilds, saving hundreds of dollars in maintenance costs per truck each year while also keeping revenue-earning equipment on the road longer. Fleets that adopt speed policies report added savings due to reduced service work, according to ATA.

IDLE REDUCTION

Driver comfort is essential to the job, so it's common practice for drivers to run their engines to stay warm or cool in their trucks when they're parked. But when idling the engine is the only way to control the cab environment, it comes at a great cost to the truck owner in terms of fuel economy. Surveys say that the average long-haul truck will idle anywhere from six to eight hours a day for as many as 250 to 300 days each year. A study on anti-idling solutions by Argonne National Laboratory states that long-haul trucks idling overnight consume more than 838 million gals. of fuel each year. EPA says fleets can save more than $6,000 per truck annually by limiting excessive idling.

On top of increasing fuel consumption, idling also increases engine maintenance costs, shortens engine life and adversely affects driver health and well-being by creating elevated noise levels and harmful emissions. Educating drivers about the impact of excessive idling on fuel consumption, the environment and potential health risks can play an important part in changing idling behavior. Many trucking companies say idle reduction incentives have been successful in keeping idling times well below national averages.

However, simply instituting a company “no-idling” policy isn't enough to deter drivers from idling in extreme weather conditions; technology solutions must also be implemented for a successful idle reduction program. There are four categories of truck technology-based idle reduction alternatives:

• Automatic engine shutdown/start-up systems control the engine by stopping or starting it without operator action based on a set time period or ambient temperature and other parameters such as battery charge. A driver can set the system to turn on the engine and heat when the outside temperature drops to 65 deg. F.

• Direct-fired heaters are small, lightweight devices that provide heat only.

• Auxiliary power units/generator sets are small, diesel-powered engines that are installed on the truck to provide air conditioning, heat and electrical power to run accessories like lights, onboard equipment and appliances. Reefer manufacturers also offer in-cab temperature-control solutions.

• Truck stop electrification refers to a technology that harnesses an electrical system to provide the truck operator with climate control and other needs, eliminating the need to idle the main engine. It can be a stand-alone system, or it can include a combined onboard and off-board system. IdleAir, the first widespread truck stop electrification project, has struggled over the years but is still in operation; however, without widespread installations of anti-idling solutions, this technology is only a partial solution to the idling issue.

REDUCING WEIGHT

Truck fuel consumption increases significantly with the weight of the vehicle. Heavier trucks require more fuel to accelerate and climb hills and reduce the amount of cargo that can be carried on the rig. Choosing lighter-weight tractor and trailer components can reduce truck weight by thousands of pounds; reducing 3,000 lbs. from a heavy truck could save between 200 and 500 gals. of fuel each year, according to SmartWay.

Generally, an empty truck makes up about one-third of the total weight of the truck, so every 10% drop in truck weight reduces fuel use between 5 and 10%. Using aluminum, metal alloys, metal matrix composites, and other lightweight components can reduce empty truck weight and improve fuel efficiency while reducing greenhouse gas emissions. Most truck manufacturers offer lightweight tractor models that are 1,000 or more pounds lighter than comparable standard models.

Lighter-weight models combine different weight-saving options including:

• Cast aluminum alloy wheels can save 40 lbs. each.

• Aluminum axle hubs can save over 120 lbs. compared to ductile iron or steel.

• Centrifuse brake drums can save nearly 100 lbs. compared to standard brake drums.

• Aluminum clutch housing can save 50 lbs. compared to iron clutch housing.

• Composite front axle leaf springs can save 70 lbs. compared to steel springs.

• Aluminum cab frames can save hundreds of pounds compared to standard steel frames.

• Downsizing to a smaller, lighter-weight engine can save over 700 lbs.

Truck trailers offer additional options for weight savings. Lightweight components that can reduce empty trailer weight by 2,000 lbs. or more include:

• Aluminum roof posts can save approximately 75 lbs.

• Aluminum floor joists can save about 300 lbs.

• Aluminum upright posts can save about 600 lbs.

• Aluminum hubs and wheels can save about 900 lbs.

Price is a consideration when spec'ing rigs with lighter-weight materials, which cost, on average, about $2,000 more than a comparable standard model. Trailer manufacturers report a similar cost premium. While lighter-weight truck options are currently more common in freight applications that are weight-sensitive, EPA says lightweight specs will be beneficial to fuel economy in any application.

IMPROVED AERODYNAMICS

Aerodynamic drag (wind resistance) accounts for most truck energy losses at highway speeds. Reducing drag improves fuel efficiency; the longer the route and the higher the speed, the greater the potential efficiency benefits. Manufacturers have made significant progress over the past two decades in reducing the drag coefficient (a measure of wind resistance) of a typical freight truck from about 0.8 to about 0.65 — an improvement of nearly 20% — according to wind tunnel studies.

Additional efforts to improve aerodynamics could result in a further 20% reduction in the drag coefficient. This could have a significant impact on fuel economy. For example, cutting drag 25% could raise fuel economy as much as 15% at highway speed. Using a streamlined tractor with aerodynamic devices will reduce fuel costs by over $800 per year, EPA estimates.

Truck-tractor aerodynamic options include roof fairings (an integrated air deflector mounted on the top of the cab), cab extenders (known as gap seals, which reduce the gap between the tractor and the trailer), side fairings, and a front bumper air dam (to reduce air flow beneath the truck). Truck manufacturers offer aerodynamic models that include a streamlined front profile, sloped hood, and a full package of add-on devices. These tractor models can improve fuel economy by up to 15% when compared to similar models without aerodynamic features. For a typical combination truck, improving aerodynamics by 15% would cut annual fuel use by up to 2,430 gals.

Trailer aerodynamics can be improved by minimizing the gap between the tractor and the trailer to reduce air turbulence. Specifying wheelbase and fifth-wheel settings that position the trailer as close to the rear of the tractor as possible can reduce tractor-trailer gap. Reducing trailer gap from 45 to 25 in. could improve fuel economy as much as 2%.

Another innovative trailer option is the use of side skirts. These panels hang down from the bottom of a trailer to enclose the open space between the rear wheels of the tractor and the wheels of the trailer. According to trailer side skirt manufacturers, use of the devices can improve fuel economy up to 5%.

Cargo “profile” is also important. On flatbed trailers, operators can reduce drag by arranging cargo as low and as smooth as possible. Secure loose tarpaulins and close the curtains on empty curtain-sided trailers to improve fuel economy by up to 2.5% and 4.5%, respectively.

Many new straight truck models incorporate a sloped hood and a more streamlined front profile in order to reduce drag. When rounded air deflector bubbles are added to trucks with van-style bodies to reduce drag, manufacturers claim fuel economy benefits of 5 to 10%. This would yield annual fuel savings of 82 to 165 gals., with high-mileage operations realizing even greater benefits.

Some aerodynamic options are standard on many trucks, like a streamlined hood, while others can be retrofitted. The initial expense of these options is often quickly recouped through fuel savings, according to SmartWay.

TIRES AND FUEL ECONOMY

Tire rolling resistance accounts for nearly 13% of truck energy use. A variety of tire options can improve truck fuel efficiency. One promising strategy is to use single wide-base tires. A single wide-base tire and wheel is lighter than two standard tires and wheels. Total weight savings for a typical combination truck using single wide-base tires on its drive and trailer axles ranges from 800 to 1,000 lbs. The weight savings would reduce fuel consumption or increase cargo capacity.

Wide-base tires have lower rolling resistance and aerodynamic drag, and generate slightly less pass-by noise than dual tires. The new generation of wide-base tires has a section width of up to 17.5 in., so these tires comply with pavement weight laws in all 50 states for a typical tandem axle combination truck. For some non-tandem axle combination trucks, wide-base tires may not comply with “inch-width” laws in certain states.

Recent tests of wide-base tires indicate a potential fuel economy improvement of 2 to 5% compared to equivalent dual tires. A single wide-base tire costs about the same as two equivalent dual tires and a single wide-rim wheel typically costs about $130 less than two standard wheels. By using wide-base tires, a combination long-haul truck could save over 400 gals. of fuel per year while cutting costs. While retrofitting existing trucks with wide-base tires and wheels may not be cost-effective, for new trucks the payback is instantaneous since the initial savings could exceed $1,000 just in tire costs alone. In addition, fuel savings begin immediately, the EPA says.

TIRE INFLATION AND FUEL ECONOMY

When not properly inflated, tires flex more under load, producing heat and increasing rolling resistance, which wastes fuel. Truck tires inflated 10 psi below recommended air pressure levels can reduce truck fuel economy from 0.5 to 1%.

Heat and stress from improper inflation also soften and deflect tire components, causing faster and more uneven wear, which shortens the life of the tire. Underinflated tires have more frequent punctures, increasing the risk of tire failures that can lead to costly road service and loss of revenue.

A recent survey on combination trucks found that less than half the tires surveyed were within 5% of the recommended inflation pressure. Truck tires can lose up to 2 psi each month, even if the rim seal and valve stems are tight. This is because air molecules can permeate through tires. Temperature and load also affect tire pressure. For these reasons, tire manufacturers recommend checking tire pressure each week and establishing a tire maintenance program.

Even a good tire maintenance program may fall short. In part, this is because trailer tires have more impact on truck fuel economy than tractor tires, yet trailers are interchangeable and harder to monitor. Since the bulk of the load is carried in the trailer, a 10-psi underinflated tire may have nearly twice the impact on truck fuel economy as the same amount of underinflation in a drive tire.

Despite the importance of keeping trailer tires properly inflated, a fleet may not be able to inspect its trailers regularly. Much of the responsibility for checking tire pressure is left to drivers; however, one industry survey indicates only 8% of drivers check tire pressure with a tire gauge before each trip.

Automatic tire inflation (ATI) systems monitor and continually adjust the level of pressurized air in tires, maintaining proper tire inflation automatically, even while the truck is moving. ATI systems can extend tire life by 8% or more and eliminate the need to check tire pressure manually, saving time and labor while ensuring consistent and proper tire inflation. For a typical long-haul combination truck, annual fuel savings could reach 100 gals. The cost of installing an ATI system in a line-haul truck is generally recouped in just over two years through fuel and maintenance cost savings, according to EPA. Automatic tire inflation systems also reduce the risk of expensive tire failure caused by underinflation.

MAINTENANCE AND LUBRICANTS

Lubricants reduce friction and wear of critical vehicle systems including the engine, transmission and drivetrain. Without lubricants, the moving parts inside these systems would grind together causing heat, stress and wear.

Low-viscosity lubricants are less resistant to flow than conventional lubricants, helping reduce friction and energy losses.

Manufacturers generally offer low-viscosity blends as “fuel economy” lubricants, since the fuel-saving potential of these products is significant. ATA reports that synthetic transmission and axle lubricants can improve fuel economy by 0.5% in the summer and 2% in the winter (viscosity is temperature-dependent). A paper published by the Society of Automotive Engineers (SAE) found that synthetic engine and transmission lubricants could improve fuel economy by 5%, with greater gains at lower speeds. Another SAE paper reports that synthetic gear lubricants can improve fuel economy by about 3%. European research demonstrates a 3 to 5% gain in truck fuel economy using low friction engine lubricants and a 1 to 4% gain using low friction transmission lubricants.

While synthetic and semi-synthetic lubricants typically cost 50% more than conventional mineral oil lubricants, for most trucks, the fuel cost savings generally outweigh the higher product cost, according to SmartWay. The combined effect of low-viscosity synthetic engine oils and drivetrain lubricants can improve fuel economy by at least 3%, saving nearly 500 gals. of fuel per year for a typical combination truck. Additional cost savings can be realized due to reduced component wear and maintenance.

HYBRID VEHICLES

Energy losses during deceleration and braking can be significant, especially in vehicles that frequently stop or slow down, like pickup and delivery trucks operating in urban areas. Engines designed to perform across a wide range of operating conditions tend to be less efficient and larger than engines designed to work within a less demanding range. Engine size generally affects the size and weight of other vehicle components, such as the radiator. Taken together, the energy losses due to braking and the extra fuel consumed by less-efficient engines and heavier vehicle components can account for 30% or more of a vehicle's total fuel use.

Hybrid powertrain technology makes it possible to optimize engine size and efficiency and capture and harness the energy lost during braking. Hybrid vehicles have two propulsion power sources. The main power source is usually a conventional internal combustion engine. Energy recaptured from braking is converted and stored until it can be reused by the second power source. The second power source generates extra power to supply boost to the vehicle when needed; for example, to climb a hill or accelerate to pass. Because the main engine no longer has to handle the full range of power demands, it can be optimized to operate within its most efficient performance range. Engine optimization generally allows the engine and related components to be downsized as well.

Hybrid technology is most beneficial to fleets that operate primarily in urban areas or in stop-and-go applications such as refuse trucks, parcel delivery trucks, airport parking shuttle vans, and utility trucks. In pickup and delivery service, truck fuel economy can be improved from 30 to 50% using hybrid powertrain technology, depending upon the type of technology and the amount of energy that can be captured from braking and deceleration and then reused. A typical step van could save as much as $1,200 in fuel costs per year, according to EPA. Benefits for an enclosed delivery van truck would be greater — at least $1,900 in fuel savings per year.

LOGISTICS

Inefficiencies in freight operations can cause trucks to travel empty, use longer or more congested routes, and idle unnecessarily. These inefficiencies increase fuel consumption and fuel costs. In some fleets, 15% or more of annual truck miles may be non-revenue empty miles. For a typical long-haul truck, this could add up to about 15,000 mi. each year, consuming over 2,400 gals. of diesel fuel. Inefficient truck routing and loading and unloading practices also contribute to excessive fuel consumption. A trucking fleet that optimizes its freight logistics can save fuel, save time, and improve productivity, generating fuel cost savings and additional revenue, according to SmartWay.

Computerized routing and scheduling software that is based on optimization models can often provide more efficient routing solutions than dispatchers can achieve on their own. This software allows routes to be constructed taking into account numerous dynamic factors that include driver hours-of-service rules, pickup and delivery schedules, vehicle size constraints, vehicle-product compatibility, equipment availability, vehicle-loading dock compatibility, route restrictions, and empty mileage.

Innovations like 24/7 shipping and receiving allow trucks to travel at off-peak times and avoid traffic congestion. With more flexibility to deliver and pick up loads, trucking companies can decrease idling, minimize time spent loading and unloading, and use their hours and equipment to haul more freight and generate revenue.

Trimming just 1% of empty miles from one long-haul truck can save over 100 gals. of fuel and increase ton-miles by nearly 20,000 per year. Reducing that same truck's idling by 5% through improved routing and loading practices could save another 100 gals. of fuel, according to EPA.