Argonne National Lab, US Dept of Energy

Vehicle Life Factors

Argonne National Laboratories, part of the US Department of Energy, conducted a study on the aggregate effects of excessive engine idling and speeding as part of overall vehicle operational costs …

ENGINE WEAR-AND-TEAR: Ideal driving speed for the average truck is 50-55mph; the power required to increase speed multiplies dramatically.

• 73% more horsepower to cruise at 60 mph

• 159% more horsepower to cruise at 70 mph

FUEL CONSUMPTION: Each mile per hour above 50 mph increases fuel consumption by one-and-one-half (1½) percent. A truck, which averages 8 mpg at 50 mph, will average 6.8 mpg at 60 mph.

EFFECT ON TIRES: Sustained speeds raise tire temperatures above the critical level, causing strength and wear properties to deteriorate rapidly. Tire wear will almost double at road speeds of 70 mph or greater.

MAINTENANCE COSTS: Gears, bearings, clutches, suspension and drive trains wear much faster at higher speeds. Increasing speed from 50 mph to 60 mph increases maintenance cost by 38%. Increasing the speed to 70 mph increases the cost by 80%.

ENGINE IDLE EFFECTS: Running a vehicle at idle speed dramatically reduces engine life; 60 minutes of idling is equivalent to between 80 and 120 minutes of driving time. The resulting loss of fuel economy from excessive idling can add up to 800 gallons of fuel annually for the average truck.

ACCIDENT AVOIDANCE: Approximate stopping distances, factoring in the reaction time for the average person driving a 2-axle truck, are listed below:

• 50 mph - 275 feet (.92 football fields)

• 60 mph - 375 feet (1.25 football fields)

• 70 mph - 500 feet (1.67 football fields)

At 70 mph, stopping distance is 63% greater than at 50 mph. Even in daylight, higher speeds will significantly increase accident probabilities.