How Low Can I Go?
A lesson in lowered fuel consumption
By David A. Kolman
There are three fundamental factors that affect a vehicle’s fuel consumption: the vehicle, driving conditions — which are outside the control of driver and vehicle — and driver operation.
Believing myself to be a fuel-conscious driver, I was excited by the opportunity to participate in an Isuzu Motors Ecology and Economy Drive program at the manufacturer’s Wacom proving grounds in Hokkaido, Japan. The event was designed to demonstrate that focusing on specific, key driving areas can appreciably reduce fuel consumption. While it involved only light-duty vehicles, the same principles demonstrated apply to medium- and heavy-duty trucks.
Isuzu Motors’ own research shows that drivers can cut fuel costs by up to 40 percent through changed habits. I routinely use fuel-saving methods, especially when I trailer-truck, so I wasn’t expecting to gain much of an improvement following the program.
We drove a three-mile course, set up to mimic highway, stop-and-go and intercity driving. Our driving was monitored by Isuzu’s Mimamori telematics fleet management system, designed especially for commercial vehicles.
We were each assigned a truck and told to drive as we normally would. We drove a similarly spec’d 136-inch wheelbase Isuzu ELF (the low cab forward N Series in the U.S.) with a gvw of 13,650 pounds. The trucks were powered by a 150 horsepower 4-cylinder Isuzu diesel backed to an Isuzu 6-speed manual transmission.
Shortly after our first run, we were given a diagnostic report of our driving behavior from the Mimamori system. The report evaluated us on five driving techniques: vehicle speed in ordinary driving, engine speed in gear upshift, selection of optimal cruising gear ratio, degree of accelerator depression, and brake application.
The report also provided an overall evaluation score, along with driving technique suggestions for fuel economy improvement.
According to my diagnostic report, I started out too “aggressively,” didn’t shift soon enough, and braked too hard a little too often. (Surely that couldn’t be right. I wondered when the Mimamori system was last calibrated.)
The next step in the program was a detailed classroom session on the whole matter of fuel consumption and conservation. Among the chief points made during the session:
• When traveling on a highway, fuel economy can be improved by 12 percent or more each time speed is reduced between five to 10 miles per hour.
• Avoiding jackrabbit starts decreases fuel consumption, particularly in stop-and-go situations.
• Maintaining a steady, consistent highway speed reduces the need for frequent acceleration and deceleration that increases fuel consumption.
• Avoid excessive use of the exhaust brake. Turn it off and plan decelerations in advance. While engine braking requires a longer distance to slow the truck, no fuel is consumed.
• Idle only when necessary.
Class over, we returned to our same trucks and ran the course a second time using what we learned. I recorded an overall fuel economy improvement of more than 30 percent.
Point taken. I guess I am now even more of a fuel-conscious driver.
Bonus: Safety Tip From Dave
We have a good idea of what’s happening on the road in front of us. But we really need to worry about what’s going on behind us. Rear-end collisions account for the largest portion of accidents on the road today. Often, this type of collision creates a chain reaction, leading to even more damage and possible injury.
There are two types of rear-end crashes: “lead vehicle stationary” and “lead vehicle moving.”
The incidence of the lead vehicle being stationary occurs at least twice as often as a moving lead vehicle, according to analyses of rear-end collisions by the Intelligent Vehicle Initiative (IVI), an organization dedicated to prevention of highway crashes and the fatalities and injuries they cause.
IVI’s data indicates that driving task errors account for the largest percentage of causal factors for lead vehicle stationary type rear-end collisions. Driving task errors can be categorized as: recognition errors (inattention, distraction and misperception), decision errors (when a driver chooses an improper action to avoid a crash) and performance errors (when a driver brakes too lightly, freezes or oversteers).
Research further indicates that the main cause of rear-end collisions is drivers not leaving sufficient distance between their vehicle and the one ahead of them in order to stop in time in case of a sudden and unexpected stop of the lead vehicle.
One general method for maintaining a safe interval between the vehicle ahead, at any speed, is what’s known as the timed interval, according to traffic safety officials. It is based on the distance a vehicle will travel in a given period of time.
Here’s how it works: Watch for the vehicle ahead as it reaches some fixed object near the roadside, such as a mile marker or tree. As the vehicle passes the object, count the seconds until your vehicle reaches that same object.
If your vehicle passes the object before you count six seconds (for a heavy duty truck), you are following too closely and should reduce speed.