January 2012, Business Fleet - Feature

Efficient Driving Equals Fleet Savings

We all know that idling and running the air conditioner can negatively affect a vehicle’s fuel economy, but a new study backs those claims with hard numbers.

By Joanne M. Tucker

Photo: ©istockphoto.com/MCCAIG

Ignoring fuel-savings strategies such as vehicle maintenance, driver training and route selection can reduce a vehicle’s cumulative fuel efficiency by about 45%, according to a study from the University of Michigan Transportation Research Institute (UMTRI).

Without any such strategies in place, the study found that a vehicle that should obtain 36 mpg will end up earning less than 20 (see table below). Fortunately, each of these factors are within a fleet manager’s and driver’s control.

Source: UMRTI 2011 study

The table shows how much efficient driving and other strategic fleet decisions can impact a vehicle’s fuel efficiency. This 36-mpg vehicle — one of the most efficient internal-combustion engine models in the U.S. at the time of the study — ends up getting only 19.8 mpg after calculating in excessive idling, route selection and other factors.

UMTRI’s analysts call these efficient driving strategies “eco-driving.” They break down the various factors that affect fuel efficiency by looking at three areas: operational decisions such as aggressive driving, tactical decisions like route selection, and strategic decisions such as vehicle maintenance.

Operational Decisions: Driving Behavior
Idling, low and high speeds, cruise control, air conditioning and aggressive driving all play a negative role on a vehicle’s fuel economy. Depending on engine size, idling uses a quarter- to a half-gallon of fuel per hour. While people are often under the impression that it’s better to idle for a minute or two rather than restart the vehicle, “it only takes a few seconds worth of fuel to restart your engine,” according to the Environmental Protection Agency (EPA).

Utilizing cruise control at highway speeds can improve fuel consumption by about 7%. Speed in general is like “an inverted U-shaped function” in terms of fuel efficiency, in which the lowest and highest speeds are the least ideal. For example, the study points out that a 2007 Honda Accord experienced its best fuel economy in a natural setting at 61 mph. Driving 30 mph below or above that speed resulted in at least a 30% decrease in fuel efficiency.