Understanding Fuel Economy

The importance of fuel economy to the successful operation of a trucking company cannot be understated. Fuel is one of the largest variable costs in a trucking venture, and, while no trucking operation can control the cost of fuel, it has at least some control over the amount or rate of consumption.

Rock-Solid Rules

• Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.
• Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 mpg.
• Worn tires provide better fuel economy than new tires, up to 7% better fuel economy.
• Used lug drive tires can get up to 0.4 mpg better than new lug tires.
• Ribbed tires on the drive axles provide 2–4% better fuel economy than lugged tires.
• Every 10 psi that a truck’s tires are underinflated reduces fuel economy by 1%.
• The break-in period for tires is between 35,000 and 50,000 miles.
• Tires make biggest difference in mpg below around 50 mph; aerodynamics is the most important factor over around 50 mph.
• The most efficient drivers get about 30% better fuel economy than the least efficient drivers.
• Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel efficiency by 1%.

Measures to Improve Fuel Consumption

Taking advantage of improved engine technology – All fleets identified this fuel saving measure. Some fleets improved fuel efficiency by as much as 10 L/100 km (about 1.5 mpg imperial) when they switched from mechanical engines to the first generation of electronic engines. When they later switched to the new generation of electronic engines, they improved fuel efficiency by a further 4 L/100 km (about 0.5 mpg imperial).

Improved vehicle specification and aerodynamics – Many fleets said that advanced vehicle aerodynamics improved fuel efficiency, in some cases by an estimated 10 percent.

Installing a fuel performance display on the dashboard and/or equipping tractors with on-board monitoring devices – Half of the fleets had installed these devices. However, they had different opinions on their impact because some drivers did not take advantage of this technology. When drivers used the information from the devices, fuel efficiency generally improved.

Driver training in fuel efficiency – Close to 70 percent of the fleets delivered some form of fuel efficiency training for drivers. In some fleets, training and information programs are ongoing.

Checking tire pressure – Close to 95 percent of the fleets checked tire pressure regularly. However, the definition of “regularly” varied significantly. Some fleets monitored tire pressure every day or after every trip, while others did so less frequently.

• Restricting vehicle speed – Policies on maximum vehicle speed varied significantly from fleet to fleet. About five percent of the fleets specified a maximum highway speed of 90 km/hr. Other fleets simply advised drivers to abide by the posted speed limit. In addition, some fleets programmed engines not to exceed a certain speed, instead of articulating a policy.

Reducing vehicle idling – About half of the fleets programmed engines to automatically shut off after 2 to 15 minutes of idling. More and more fleets appear to be taking advantage of this option, which is now available for all electronic engines. At the same time, many fleets left idling to the discretion of drivers, who may idle the engine to warm or cool the tractor while they sleep. Fleets that allow this practice can experience higher idling rates.

Driver incentive programs – Ten of the 42 fleets offered some form of driver incentive program. However, only four fleets had a full incentive program with rewards; the other six posted the best fuel consumption results of drivers over a set period of time. Several fleets were considering incentive programs.

• Regular vehicle maintenance – Although all fleets had regular maintenance programs, their effect on fuel efficiency is difficult to quantify. Some fleets estimated that regular maintenance may have improved fuel efficiency by up to 1.5 percent.

Downloading information from engines – More than 75 percent of the fleets regularly downloaded information from vehicle engines. The interval between downloads varied from fleet to fleet; these were often done when a vehicle was scheduled for maintenance. Large fleets appear to download engine data more frequently than smaller fleets.

Use of add-ons – Thirteen fleets used add-ons such as cab heaters. These fleets also tended to have an idling policy.