Fuel economy varies dramatically depending on so many factors, including your truck's make and model, trailer's weight, driving route, and so much more. You may be looking for that one add-on, or that single silver bullet, that would improve your fuel economy. Unfortunately, it simply doesn't exist. While there are dozens of mechanical or electronic gizmos you could deploy to bump up your fuel mileage in some small way, the most effective measure is in fact you, the driver.

It is possible to put two drivers on two identical trucks and see a difference of up to 30 percent in fuel economy. Much of that chasm stems from good or bad pedal and stick management, and drivers' willingness to use available technology to their advantage. 

You have likely heard the claims made by the purveyors of autonomous - or driverless - trucks, in that they will save fuel and reduce greenhouse gas emissions. Autonomous trucks will deliver on that promise through very precise throttle and vehicle speed management, the correct gear choices, and absolute constant adherence to the mission. Few human drivers could ever match a computer for fuel efficiency because we could never maintain that level of concentration for every minute of an entire driving shift. 

The best example of that thinking is automated manual transmissions (AMT). For years, skeptics asked how a transmission could make a difference. It was just a box full of gears. The difference is that the computer controls the shifting, not the driver. 

Fleets lauded AMTs as "the great equalizers." They did wonders for the worst drivers, and the best drivers often got even better results. But there's more to it than just being more precise in getting the stick into the right slot more often.

Engine Control Models (ECMs) are calibrated to optimize fuel economy by hitting the right shift points more often than poor drivers can seem to manage. But a good driver can easily out-drive an automated transmission. The driver can see, while the ECM cannot. The driver can manage, while the ECM can only respond. 

Throttle Management

The idea is to use the least amount of fuel possible to get the job done. That applies at cruise speed as well as when shifting up through the gears. Every drop of fuel you put through the engine that it doesn't need is fuel wasted. The goal is to use the absolute minimum amount of fuel to get the engine speed up to the next gear change. 

With a manual transmission, there's really no need to exceed 800-1,000 rpm in the first four or five gears. There's enough torque between idle and 800-1,000 to accelerate the truck to the next upshift. Gentle upshifts at low rpm conserve fuel. That‚Äôs what AMTs are programmed to do. 

Award-winning journalist, host of HDT Talks Trucking podcast, and writer of this article, Jim Park illustrates the importance of throttle management through a personal experience: "The value of gentle throttle application was demonstrated to me several years ago in a thoroughly instrumented truck provided by a popular truck maker. I was to compete against another driver in a fuel economy competition. We both drove the same truck over the same 496-mile route, with a second truck following along to monitor weather, wind, traffic, etc. so the results could be "normalized."

The other driver beat me in overall fuel economy (adjusted for weather, and other factors) by 0.27 mpg. My average speed was 49.8 mph, while his was 50.6. My average engine rpm for the trip was 10 rpm higher than his, and my average turbo boost was 10.1 psi compared to his 9.6.

While the results weren't much different, throttle-position data from the ECM showed the other driver was less aggressive with the throttle pedal than I was. He earned his victory by treading easier on the throttle pedal while going up and down through the gears. 

As further proof of the benefit of gentle throttle pedal control, I offer Jim Booth. He was a test pilot for Caterpillar back in the 80s and 90s, and a zealot on fuel economy. He hauled freight for Cat between northern Wisconsin and Cat's headquarters in Peoria, IL. The company benchmarked their engines against his performance. Even back then, before all this fancy new technology was even thought of, Booth consistently got 9.3 mpg out of his C13 engine. 

His style was to step so easily on the pedal that you'd swear it was made of crystal. Most drivers would call his acceleration painfully slow, and his adherence to 55 mph nearly unbearable, but you can't argue with 9.3 mpg (US) fully loaded.   

Be Careful with Cruise Control

Cruise control is a great tool for maintaining a steady speed on level ground, but it can work against you as well. This is because trucks that are less than three or four years old may have been spec'd with adaptive and/or predictive cruise control options. If your truck has either or both, and you use them, you'll have an advantage over drivers with just basic cruise control, but as we've been discussing, neither of those two technologies is perfect either.

Basic cruise control is designed to maintain road speed, but it can't tell the difference between a hill and a headwind. All it knows is some external force is conspiring to slow the truck down. Cruise control will feed as much fuel to the engine as needed to maintain the set road speed. 

A driver can make a difference by backing off the throttle pedal when full power isn't needed -- like when cresting a hill. Cruise control will maintain full power until the truck is over the top and accelerating down the other side. At some point, once the set speed has been exceeded slightly, it will switch on the engine brake. So, you burn a whole lot of fuel to get over the top and then you throw on the brakes.

A more economical approach would be to climb the hill with cruise switched off so you can manage the throttle and road speed. Giving up a bit of speed won't affect your trip time, but it will save fuel. 

When you get close to the crest, back off the throttle and use as little fuel as necessary to ease over the top. Again, you'll give up some speed, but you will make it all back coasting down the other side -- free. 

Most versions of predictive cruise control have preloaded terrain maps, so with GPS, the truck's computer knows where it is and can "see" hills. It can then manage the gear shifts accordingly. Predictive cruise will do a much better job than basic cruise control, but a driver who is aware of his or her surroundings and actively working at fuel economy will do even better than predictive cruise control.

Many newer trucks will also have engine-brake-on and -off settings built into the cruise control. It is thought that these are primarily for managing company drivers. In reality they hurt fuel economy by minimizing the benefits of momentum.

Maintain Momentum

It takes a lot of energy to get 40 tons of truck up to speed; it's a shame to throw that away when an opportunity comes along to coast downhill for a spell. Being mindful of speed limits and safe operating speeds, letting the truck run out downhill will give you momentum for the climb up the other side. You can use that extra speed to delay reapplying the throttle as long as possible, thus saving fuel. 

Momentum matters in traffic too. If you have a tendency to follow too closely, you'll always be on and off the throttle to adjust vehicle speed. You get up close, then back out of it, and then throttle up to close the distance, etc. Every time you accelerate to catch up, you're wasting fuel. A more economical approach is to back out of it, let the other vehicle get far ahead, set your cruise and motor along.

If your truck is equipped with adaptive cruise control, you can set a following distance. The ECM, using data from onboard cameras or radar, will maintain that set following distance using throttle and engine braking. But adaptive cruise control is only as good as the human driver it's following. If that driver is on and off the throttle aggressively, your adaptive cruise control will follow accordingly.

Everything offered or suggested here comes with a decision the driver has to make. It would be easy to keep the cruise control on and let the ECM do all the work, but a driver who is working at fuel savings will out-drive cruise control every time. Slowing down will always save money, but of course trip times and ELDs are a factor. Developing better shifting habits and accelerating more slowly will save money too. And this goes even for drivers with automated transmissions. The shift algorithms take cues from how aggressively the pedal is pressed down. Go easy on the pedal and you'll go easy on your wallet, too.

You, as the driver, are the single biggest factor in fuel economy. Turn off the engine when not using it and going easy on the throttle pedal will certainly save you money.

Other relevant articles:

Fuel Economy: Part 2 - Maintaining Existing Equipment

Fuel Economy: Part 3 - Investing in New Equipment

Understanding Diesel Engine Oil Viscosity and the Best Oil for Your Truck