California Air Resources Board

Various aerodynamic improvement technologies have been evaluated through the U.S. Environmental Protection Agency (EPA) and California Air Resource Board's (CARB) programs including U.S. EPA Phase 1 and CARB’s Tractor-Trailer Greenhouse Gas (GHG) Rule.  The vast majority of these technologies have devices primarily intended for heavy-duty Class 8 long-haul tractor-trailers, leaving a data gap regarding the potential benefits of aerodynamic improvement technologies for use on medium-duty vocational vehicles.

The National Renewable Energy Laboratory (NREL) under CARB Agreement performed a series of coastdown and constant-speed on-highway tests on medium-duty vocational vehicles with and without aerodynamic improvement devices to assess their performance. The report, "Aerodynamic Drag Reduction Technologies Testing of Heavy-Duty Vocational Vehicles and a Dry Van Trailer" indicated adding an aerodynamic improvement device or combination of devices to certain types of vocational vehicles can result in a measurable fuel savings and emission benefits. However, the precise benefit realized under real-world driving conditions is strongly dependent on the vehicle drive cycle. Because vocational vehicles are used in such a wide array of applications, vehicle build specifications alone may not be sufficient to predict aerodynamic benefit, but certain drive cycle characteristics such as kinetic intensity have demonstrated a very strong prediction capability. Hence, in the final federal Phase 2 GHG regulation for medium- and heavy-duty vehicles, the U.S. EPA and the National Highway Traffic Safety Administration allow optional emission credits for installing aerodynamic devices on regional vocational vehicles, depending on eligibility criteria.

Accurate characterization of vehicle activity is critical to the development of appropriate air quality strategies.  In pursuit of this goal, CARB has already funded a study conducted by University of California, Riverside College of Engineering-Center of Environmental Research and Technology which compiled the following report, “Collection of Activity Data from On-Road Heavy-Duty Diesel Vehicles”. This study provided some critical information on heavy-duty trucks and included information about specific vocational vehicles but more in-depth information on these vehicles is necessary to understand the potential benefits of aerodynamic devices.  Specifically, detailed information on Class 4-6 (Gross Vehicle Weight Rating 14,001 to 26,000 lbs.) heavy-duty vocational vehicle population such as vocation and type and more studies of the activity of these vehicles is needed to access the statewide impact aerodynamic improvement devices could have on heavy-duty vocational vehicle fuel economy.

Recently, CARB contracted with NREL and  University of California Irvine to provide CARB additional information about the details of the vocational fleet and how heavy-duty vehicles are used in the state of California through a survey and data collection exercise. This information is critical to understanding the nature and operations of vocational vehicles in California and the potential for incentives and regulations to encourage the use of aerodynamic devices to reduce GHG emissions from these vehicles.

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