Image: University of Michigan |
While driving a fuel-efficient vehicle is the best way to
save gas, motorists can still cut fuel consumption nearly in half by driving
slower and less aggressively, properly maintaining their vehicles, and avoiding
congested roads, say University
of Michigan researchers.
“Driving a light-duty vehicle in the United States
is currently more energy-intensive than using a bus or a train and even
flying,” says Michael Sivak, research professor at the U-M Transportation
Research Institute. “How can we improve on this performance? Vehicle
selection has by far the most dominant effect—the best vehicle currently
available for sale in the United
States is nine times more fuel-efficient
than the worst vehicle.
“Nevertheless, remaining factors that a driver has
control over can contribute, in total, to about a 45% reduction in the on-road
fuel economy per driver—a magnitude well worth emphasizing.”
Sivak and colleague Brandon Schoettle studied the effects of
decisions that drivers can make to influence on-road fuel economy of light-duty
vehicles. These eco-driving practices include strategic decisions (vehicle
selection and maintenance), tactical decisions (route selection and vehicle
load), and operational decisions (driver behavior).
The UMTRI researchers say that choosing to drive a car (23.7
average mpg for model year 2011) rather than a minivan (19.4 mpg), SUV (19.2
mpg), or pickup truck (17.2 mpg) may be the easiest way to save gas. However,
regardless of vehicle type, drivers who keep their engines tuned, tires
properly inflated, and use the right kind of engine oil can improve fuel economy
by as much as 40%.
Further, by choosing to drive on routes that include
highways, flat terrain, and less congestion, motorists can save gas. For example,
a flat route can yield 15 to 20% better fuel economy than a hilly route and
taking a free-flowing highway route as opposed to a highly congested route can
improve fuel economy for that trip by 20 to 40%, the researchers say. In
addition, carrying extra cargo (e.g., an additional 100 lbs), can reduce fuel
economy by up to 2%.
Finally, Sivak and Schoettle say that driver behavior can go
a long way in improving fuel economy. Driving slower and less aggressively can
save motorists up to 30% in gas usage, while turning off the air conditioner
can save up to 25% and using cruise control can save 7% while at highway
speeds. In addition, letting a vehicle idle for more than a minute can
significantly reduce fuel economy.
The actual fuel savings that good eco-driving practices will
yield, however, are dependent on specific and sustained conditions.
Consequently, according to Sivak and Schoettle, the actual total savings will
be less than the sum of the listed maximum savings for each individual
eco-driving practice.
By disregarding good eco-driving practices, drivers of the
most fuel-efficient car with an internal combustion engine (36 mpg) could see
their fuel economy drop below 20 mpg—although this is still better than the
least fuel-efficient car driven according to all good eco-driving practices,
the researchers say.
“This can be interpreted as the cup being half full or
half empty,” Sivak says. “On one hand, one can conclude that
decisions concerning vehicle-selection are dominant for on-road fuel economy.
On the other hand, one can also conclude that following the remaining good
eco-driving practices can still lead to a major reduction in on-road fuel
economy.”
The researchers say their analysis focused on fuel economy
per vehicle, not per occupant. However, the average occupancy of a light-duty
vehicle has dropped from 2.0 in 1960 to 1.4 today.
“This represents a 30% drop in vehicle fuel economy per
occupant,” Sivak says. “Consequently, increased carpooling, to at
least the level of the 1960s, would go a long way to improve energy intensity
of driving per occupant.”
