FORT LAUDERDALE, Fla. - With energy experts saying retail diesel fuel prices will remain high for the foreseeable future, it continues to be smart business for coach operators to take steps to boost fuel economy in their buses.

An 18-month, telematics-based study of commercial vehicle fuel economy conducted by a fleet management and ground transportation support services company has identified several fuel-saving tactics that go beyond the usual focus on reducing speeding and idling.

The study by Fort Lauderdale-based PHH FirstFleet resulted in this hypothesis:

By slightly over-spec'ing engines to run more consistently in the "sweet spot," choosing a gear ratio low enough to suit a fleet's application and location, and enabling the correct fuel-efficient, engine-specific parameters, fuel economy can be improved by around 5 percent.

The study's findings supported the hypothesis.

When combined with other variables, including progressive shifting, the engine "sweet spot" is where both performance and fuel efficiency are maximized, resulting in measurable fuel savings.

Operators of commercial vehicles are facing a number of challenges, observes Michael C. Lewis, president and general manager of PHH FirstFleet. These include tougher emissions standards, the introduction of ultra-low-sulfur diesel fuel and new vehicle requirements.

"This study points to fuel-saving initiatives other than driver habits, such as speeding and idling, to help reduce operating costs," said Lewis.

Bus & Motorcoach News asked long-time coach industry maintenance guru Scott R. Crawford, fleet support central zone manager for Motor Coach Industries, for his comments on various aspects of the PHH FirstFleet study.

Here are the key findings from the study, along with Crawfords observations, that will help coach operators achieve better fuel economy:

1. Increase engine torque rating. Increasing the engine torque rating provides a simple and effective method to decrease time spent in the high- output torque range. Driving at high-output torque ratings leads to over-revving, or RPMs higher than the engine parameters specify. Over-revving shortens the life of the engine, sustains lower fuel economy and higher costs.

On the same note, driving in a lower RPM range than the engines specified parameters may result in driver dissatisfaction and could require increased downshifting, which indirectly causes over-revving.

Notes Crawford: "Operators need to spec the highest horsepower rating as possible." He adds, however, that coach operators usually dont have a lot of options to choose from.

2. Decrease rear-axle gear ratio. Choosing a lower gear ratio improves fuel economy, reduces engine wear, increases speed at lower RPMs and may help reduce over-revving. In general, choose the correct rear-axle gear ratio for the fleet's application and needs, but consider that while higher gear ratios may improve overall performance and provide added power in lower gears, additional power causes equipment to lose fuel economy. If improving fuel economy remains a priority, consider whether the extra performance validates the loss in fuel economy.

Adds Crawford: "There aren't too many choices engineered into coaches."

3. Engine-specific parameter controls.

A. Speeding. Above 65 mph, the engine works harder to overcome aerodynamic drag. In fact, it demands more than 50 percent of the engine's total available horsepower, which significantly increases fuel consumption. If speed is decreased to 55 mph in the appropriate gear, the horsepower demand is reduced, drawing less fuel.

B. Idling. Idling achieves 0.0 mpg and uses .5 to 1 gallon of fuel per hour. Consider idle shutdown to save fuel while at stops.

Says Crawford: "Speeding and idling are something we need to push. Speeding especially. There is a huge impact (on fuel economy) if operators would slow down their units instead of running up against the top-speed setting. Idling is tough during certain times of the year, however."

C. Progressive shifting. Drivers shifting quickly in lower gears prevents over-revving, which decreases fuel consumption and increases fuel economy.

Notes Crawford: "You really need the ZF unit to do so. The transmission ECU keeps the RPM closer to the desired range because of increased ratios and the ability to skip shifts

4. Lower weight. New materials allow for less weight and more potential fuel economy gains.

Observes Crawford: "Weight reductions are hard to achieve. Aluminum rims help and composites help but are hard to retrofit."

5. Low-profile radial or single-wide tires. Research indicates that fuel economy can improve from 2 percent to 5 percent by using low-profile and/or wide-based tires and wheels. Decreased weight and lower rolling resistance are the key contributors to fuel economy improvements.

Asserts Crawford: "Single drive tires sound great on the surface as a possibility to cut costs but there are some issues that reduce the feasibility on a bus. No spare tire can be stored in normal locations, availability of replacements on the road, safety on blow outs and the like."

6. Tire pressure settings.

Says Crawford. "Proper tire pressure settings are critical. SmarTire systems will help operators, as well as providing additional safety for the coach."

"A big plus to all these changes in fuel prices, as well as the increased awareness of environmental concerns, is that they should . . . help the industry expand business," said Crawford.