When it comes to figuring out how to benefit from the fuel economy improvements purportedly being offered by greenhouse gas (GHG) regulations, fleets are finding that a lot of hard-to-calculate factors are involved, especially in terms of driver behavior.
“The biggest piece of fuel economy performance we’ve yet to really tap is the driver,” Glen McDonald, director of maintenance at Ozark Motor Lines, explains. “We give drivers all the tools—automated manual transmissions (AMTs), cruise control, etc. But radar [based cruise control] makes the truck stay back farther than they like. So how do we get the driver to sit back and let the truck do more of the work?”
It’s also about compensating for other external factors, he says, such as seasonal differences, road type, road conditions, and even the direction of the wind.
“I have a guy—one of my best drivers—who makes a run from Memphis to St. Louis and back. You can take his trip data and calculate his fuel mileage to a tenth of a mile every day,” McDonald says. “He can also tell you about real-world impact, such as tailwind, giving him 1 mpg better heading down to St. Louis.”
That doesn’t stop Ozark from spec’ing its equipment as fuel-efficiently as possible with improved aerodynamics, McDonald stresses. Right now, the company operates a little over 700 Freightliner Cascadia tractors spec’d with the full Evolution aerodynamic package, a Detroit DT12 AMT mated to DD15 engines, and fuel-efficient tires. All of its 53-ft. dry van trailers are equipped with side skirts.
The fleet has even switched to full synthetic yet thinner viscosity motor oils. Longer change intervals allow the company “to get more fuel mileage from them with less maintenance,” McDonald notes.
Yet figuring out the role of specific pieces of the fuel-saving equation, i.e, AMT, trailer skirts, etc., is the tricky part. “We’re doing so many things at once. How does each piece contribute?” McDonald points out. “We really rely on our partners to help us pick the best specifications and solutions. We have to trust them. But I still have to use simple math to make it work. It has to pay out in the end.
“And the real world is very different than the test track,” he continues. “It’s also hard to figure [those specific savings] with different drivers in different weather conditions on very different roads.”
Paul Higgins, director of maintenance at Prime Inc., also struggles with similar questions and finds that the company requires a two-step solution that involves a focus on equipment specifications and on driver training.
“We have classes to teach drivers how to be the most fuel efficient. [It’s] a fairly straightforward process and not necessarily a magic pill,” he points out.
In terms of equipment, Higgins says Prime specs its trucks and trailers to be as “slick” as possible.
“Aerodynamics offer a huge opportunity for all of us to improve fuel mileage. We also realize we’re not doing all that we can to be more aerodynamic,” he explains. “Based on our model, it’s crazy to spec a ‘square hood’ truck now.”
Higgins points out that trailer skirts offer 6% fuel savings and can get up to 9% in some cases. “Since we make our own skirts, we can make modifications based on how we see them work,” he adds.
Researchers are also starting to put some numbers to aerodynamic improvements. The latest Confidence Report compiled by the North American Council for Freight Efficiency (NACFE), for example, determined that aerodynamic enhancements to Class 8 tractors can return a sizable saving in fuel efficiency—even for day cab models that many felt were incapable of benefiting from aerodynamics.
“During the past 20 years, truck manufacturers have done a good job of improving the aerodynamics of sleeper tractors, saving up to 10% in fuel costs,” the group notes in its Tractor Aerodynamics Report. “Tractor aerodynamic devices improve fuel efficiency by reducing drag so that it takes less fuel to move down the road, especially at higher speeds.”
Even though day cab tractors operate at lower miles per hour, NACFE researchers found they benefit from the installation of aerodynamic devices.
“There is a long-standing misperception in the trucking industry that improved aerodynamics will only save fuel at speeds above 55 mph. Because of this, day cabs and other [tractor] duty cycles have lagged long-haul sleepers in their aerodynamic performance improvements,” the group notes.
“But in reality, aerodynamic drag is acting against the vehicle at all speeds above zero mph. Given the many low- or no-cost design elements that can reduce drag, even fleets operating at lower speeds should consider adoption,” NACFE adds.
Mike Roeth, the group’s executive director, believes truck manufacturers should make full aerodynamic packages like those offered on sleeper cabs standard on their day cab tractors.
“Not only do those packages provide substantial fuel economy benefits even at lower speeds, but fleets tend to have much longer trade cycles for their day cab trucks,” he says. “The fuel savings over a decade can also help fleets limit the risks of future diesel price increases.”
Other findings from the NACFE Tractor Aerodynamics Report include the following:
- If aerodynamic features are removed from an OEM’s aerodynamic base model, the fleet can expect to lose about 10% in fuel economy.
- Another 10% can be lost simply by pairing a mid-roof tractor with a dry van or refrigerated trailer. NACFE stresses that tractor and trailer heights should be matched for as many miles as possible.
- Even at today’s fuel prices of around $2/gal., a 10% savings in fuel represents $3,500 per year per truck.
- The greatest opportunity to benefit from aerodynamic tractor enhancements remains the on-highway van trailer segment for both day cabs and long-nose high-roof sleeper models.
- While the devices currently available on the market do add some weight to the vehicle, the impact of the weight on fuel economy is just 0.5 to 0.6% per 1,000 lbs.
- There is less than a 2,000-lb. weight difference between the most aggressively optimized aerodynamic tractors and the least, so the maximum mpg reduction due to aerodynamics is less than 1.2%—far smaller than the potential fuel savings offered by aerodynamic enhancements.
- Many day cabs operate at highway speeds during nearly all of their duty cycle, so aerodynamic styling can increase fuel efficiency for day cab models by as much as 13%. Even day cabs operating in start-stop city driving will see savings from certain aerodynamic technologies, NACFE found.
Consider all costs
Consulting firm Fleet Advantage takes all of that a step further with a new data index resource it has compiled. John Rickette, vice president of transaction management, notes the resource compares “all-in” costs of older model-year Class 8 trucks and calculates the savings of new model replacements to help fleets identify the sweet spot for replacement and which specs may add the most cost savings.
That all-in approach means taking into account operating costs related to fuel, finance, maintenance and repair, and tires, he explains.
“When you do that, you are looking for the point in time when a truck becomes economically obsolete,” Rickette says. “There’s always an inflection point, but that also depends on miles driven, type of duty cycle, etc. Roughly between 400,000 and 500,000 mi. is the sweet spot. That is when maintenance and repair costs spike; there’s degradation in fuel economy; resale value spikes; and warranty coverage begins to expire.”
Using its index, Fleet Advantage calculates that companies using Class 8 trucks would save approximately $18,000 per truck in the first year by upgrading from a 2011 to a 2017 model-year day cab or sleeper unit while reducing carbon dioxide emissions by 14%.
Rickette does note that such calculations need to be addressed on a case-by-case basis to account for variables such as usage patterns and weather.
“The first six months represent the break-in period, so fleets may not be getting [the fuel economy gains] they expect to be getting. That also applies to the seasons, as winter can affect performance,” he emphasizes.
On top of that, Fleet Advantage also plans to incorporate engine idle time, excessive speed, hours of operation, and other factors that affect vehicle wear and tear over the truck’s life cycle. “We’ll bake that in for the future,” Rickette notes.
Ozark’s McDonald stresses that when fleets try to project any sort of fuel savings, they must include items such as potential accident and repair costs.
“You’ve got to consider those,” he says. “For example, trailer tails save money on fuel for certain; however, one fleet I work with found that they got torn up so much that the cost of repairing them could make the fuel savings a wash. That’s got to be factored in.”
What’s the ultimate ingredient for maximizing fuel economy no matter the fuel-efficient specification? According to Prime, this ingredient affects about 80% of the fuel economy equation—and that’s the driver.
So, anything that can be done to ease back on the vagaries of human behavior behind the wheel will help further boost fuel economy gains down the road.
“We finally agree that AMTs can equal the best driver using a manual. AMTs are nice, fast, and smooth in terms of gear shifting now and are not nearly as herky-jerky as they once were,” Prime’s Higgins says. “Using GPS technology to adjust the truck to the topography is the next step; going around a corner, shifting in neutral because [the transmission] knows from GPS what the road is like there.”
At the end of the day, Prime says, it all comes down to engine speed; driving the engine “slower” in terms of rpm makes a big difference not just in fuel consumption but also in safety and driver comfort.
“The driver arrives more relaxed than before, not to mention accident-free. That’s a huge win,” Higgins says.