Matthew Rodriquez 

Secretary for 

Environmental Protection 

April27, 2015 

Mr. Arvon Mitcham 

Air Resources Board 

Mary D. Nichols, Chairman 

9480 Telstar Avenue, Suite 4 

El Monte, California 91731 • www.arb.ca.gov 

Program Manager/Engineer, Light-Duty Vehicle and Small Engine Center 

United States Environmental Protection Agency 

2000 Traverwood Drive 

Ann Arbor, Michigan 48105 

Dear Mr. Mitcham: 

Edmund G. Brown Jr. 

Governor 

I am writing to respond to U.S. Environmental Protection Agency's (U.S. EPA) request 

for information about Air Resources Board's (ARB) planned pup trailer aerodynamic 

testing. To support the Phase 2 heavy-duty greenhouse gas rulemaking , ARB added 

funds to an existing agreement (Agreement Number 11-600) with the National 

Renewable Energy Laboratory (NREL) (Contract Number FIA-11-1763) so that NREL 

could perform a series of tests to explore the potential benefits of using aerodynamic 

improvement devices on "twin pup" trailers in combination with a class 8 diesel powered 

tractor. Upon completion of the project, the results will be provided to U.S. EPA and the 

National Highway Traffic Safety Administration for potential inclusion in the Phase 2 

rulemaking. 

Background 

Various aerodynamic improvement technologies have been evaluated through the U.S. 

EPA's SmartWay program. The majority of these technologies have focused on devices 

intended for heavy-duty class 8 tractor-trailers in a standard single trailer (48-foot or 53-

foot) configuration. It is the intention of this NREL project to complement previous work 

and explore the potential benefits of using aerodynamic improvement devices on a long 

combination vehicle, more specifically 28.5-foot "twin pup" trailers. 

Summary of NREL Test Project 

Planned testing will utilize a class 8 diesel powered tractor in combination with a set of 

28.5-foot "twin pup" trailers. The aerodynamic improvement devices to be tested include 

trailer side skirts and a rear tail fairing. Below is a list of configurations to be tested: 

• Baseline: tractor, two pups, no aerodynamic improvement devices; 

The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. 

For a list of simple ways you can reduce demand and cut your energy costs, see our website: http://www.arb.ca.gov. 

California Environmental Protection Agency 

Printed on Recycled Paper 
Mr. Arvon Mitcham 

April27, 2015 

Page 2 

• Trailer side skirts on the front trailer only; 

• Trailer side skirts on the rear trailer only; 

• Trailer side skirts on both trailers; and 

• Trailer side skirts on both trailers and an advanced trailer tail on rear trailer only. 

All testing will include an appropriate vehicle warm-up period in order to bring the 

engine, transmission, rear differential and bearing temperatures up to their normal 

operating range. The test vehicle will be instrumented with data recording devices 

capable of logging J1939 CAN parameters of interest and a global positioning system to 

record speed and position at a minimum of 5-Hertz. Testing is tentatively scheduled to 

begin mid-May 2015 and continue through the end of June 2015. We expect the testing 

to be completed as scheduled but delays are possible depending on vehicle/trailer 

rental lead times and weather conditions. 

If you have questions or need additional information, please contact Ms. Kim HeroyRogalski, Manager, at (916) 327-2200, or email at kheroyro@arb.ca.gov or me at 

(626) 575-6632, or email at mcarter@arb.ca.gov. 

Michael Carter, Chief 

Mobile Source Regulatory Development Branch 

California Air Resources Board 

cc: Kim Heroy-Rogalski, Manager 

Strategic Planning & Development Section