this results in higher fuel consumption, and more just-in-time shipping can lead to dramatically higher fuel consumption (for example, by favoring shipping by air or truck instead of by ship or train). The white paper addresses this topic (DOE-DOT, 2011, pp. 1-2).

6.   Infrastructure improvements. Changes to increase road capacity and reduce congestion have a direct effect on truck fuel consumption. Congestion leads to more frequent speed changes and additional idling, both of which cost fuel.

7.   Intelligent transportation systems (ITSs). A wide range of features and technologies falls under the term “ITS.” These include driver information systems that can provide warning of accidents or congestion and suggest alternative routes. They can involve demand-management features that restrict access to highways prone to congestion. ITSs also include optimization of traffic-signal operation that can increase capacity, reduce congestion, and reduce speed fluctuation, all of which reduce fuel consumption. “On demand” traffic-signal switching using vehicle presence detection for control is increasingly used to reduce wait times (and fuel consumption due to idling) at stops. Changes such as traffic-signal optimization are particularly attractive, because no road construction or change to the vehicle fleet is needed for all vehicles on the route to benefit. Other ITS applications include ramp metering to reduce congestion, electronic on-road toll collection, automated electronic screening such NORPASS and PrePass for weight and safety inspections, credential checking and border clearance, among others (NRC, 2010, pp. 168-171). These applications can save fuel by reducing congestion and eliminating the need for starting and stopping. ITSs can include vehicle-to-vehicle (V2V) communication as well as V2I communication. ITS features that require V2V or V2I communication will take time to implement, because not all vehicles will have the required systems onboard. However, in many cases the overall traffic flow will benefit even if only a portion of the vehicles involved are actively using ITS. The white paper addresses ITS issues (DOE-DOT, 2011, pp. 7-9).

8.   Driver training. In order to obtain a commercial driver’s license (CDL), drivers of commercial vehicles go through more rigorous training than is required for drivers of light-duty vehicles. The primary focus of this training is safety, which misses an opportunity to train drivers in how to operate their trucks in the most fuel-efficient manner. Some truck fleets do have their own driver-training programs. These programs usually go beyond CDL requirements, and often fuel efficiency is part of this training. In some cases, engine and truck manufacturers work directly with fleet operators to help them provide the best possible information to drivers. However, at this time, there is no standardized curriculum for this kind of training, and many drivers do not receive any fuel efficiency training at all. Also, it is unclear how far such training could be standardized, in view of the many manufacturer-specific features and characteristics that drivers need to understand. Driver training is mentioned in the introduction of the white paper, but is not discussed in any detail. However, the white paper does suggest that research into aspects of driver behavior that might affect the fuel-saving performance of specific driver management features (see item 9 below) would be useful (DOE-DOT, 2011, pp. 12-13).

9.   Driver-management features. Engine and vehicle manufacturers have developed a wide range of control features aimed at encouraging (or forcing) drivers to operate in a way that reduces fuel consumption. Driver-management features are not discussed in the white paper in any detail, but they offer significant potential for fuel savings. Examples of these features include the following:

a.   Progressive shift. This feature reduces the maximum engine speed available in the lower gears, which forces the driver to shift to a higher gear earlier than he or she might otherwise choose. Cummins offers a more sophisticated version of progressive shift called load-based speed control. The control algorithm estimates the vehicle mass and the grade and adjusts the engine-speed governor to be appropriate for the vehicle load.

b.   Gear-down protection. At cruising speed, it is typically possible to operate in more than one gear. For example, it may be possible to run at 65 mph in both 9th and 10th gears with a 10-speed transmission. The gear-down protection algorithm reduces the maximum vehicle speed that can be attained in 9th gear, forcing the driver to shift to the more economical 10th gear if he or she wants to run at 65 mph. With gear-down protection, the lower gears are reserved for conditions that require their use, such as climbing hills or coming up to cruising speed.

c.   Road-speed governors. Virtually every truck sold today includes a road-speed governor, but the use of the governor and the governor setting are left up to the owner. The road-speed governor limits cruising speed. Because fuel consumption increases with cruising speed, the use of a governor saves fuel. Note that there are tradeoffs: to the extent that speed is reduced, trip times will increase. This will lead to a need for more trucks to deliver the same quantity of freight per day. Speed governors also have no effect on fuel consumption when other constraints such as congestion or road conditions limit vehicle speed so that it is at or below the speed-governor setting (NRC, 2010). Many owners of large fleets set their road speed governors in the range of 62 to



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement