Office of Operations Freight Management and Operations
photos of truck, cargo ship, airplane and freight train
Office of Operations  -  21st century operations using 21st century technologies

Aerodynamic Device Compliance with 23 CFR 658.16(b) (4)

PDF Version, 87KB
Contact Information:

DOT Logo

U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Avenue, SE.
Washington, D.C. 20590

October 10 , 2008

In Reply Refer To: HOFM-1

Mr. Andrew Smith
Chief Executive Officer
Advanced Transit Dynamics, Inc.
245 Utah Avenue
San Francisco, CA 94080

Dear Mr. Smith:

This is in response to your letter of August 21 which requested a determination of compliance of your 'Trailer Tail' aerodynamic device with 23 CFR 658.16 'Exclusions from Length and Width Determinations.' The Federal Highway Administration (FHWA) acknowledges that ATDynamics 'Trailer Tail' was tested by an independent laboratory, KARCO Engineering, and was found to be in compliance with all elements of 23 CFR 658.16(b) (4). Therefore, in accordance with Federal regulations, the ATDynamics 'Trailer Tail' aerodynamic device should be excluded from the length measurements for commercial motor vehicles.

The full test report results from KARCO Engineering were received from ATDynamics on August 25, 2008. The 'Trailer Tail' device was evaluated for compliance with the following provisions of 23 CFR 658.16(b)(4), which exclude an aerodynamic device from the measured length of a commercial motor vehicle provided:

  1. the device is not capable of carrying cargo;
  2. the device does not extend beyond 5 feet of the rear of the vehicle;
  3. the device does not obscure tail lamps, turn signals, marker lamps, identification lamps, or safety devices such as hazardous material placards or conspicuity markings;
  4. the device has neither the strength, rigidity nor mass to damage a vehicle, or injure a passenger in a vehicle that strikes a vehicle so equipped from the rear.

KARCO Engineering determined that the ATDynamics 'Trailer Tail' aerodynamic device 'Passed' all of the conditions listed in the regulation, and FHWA accepts those test results. We shared these test results with the Federal Motor Carrier Safety Administration (FMCSA) and the National Highway Traffic Safety Administration (NHTSA) for their review. NHTSA identified a conspicuity marking issue that was shared with Mr. Geoffrey Johnson, Director of Regulatory Affairs with ATDynamics, and Mr. Johnson subsequently advised us ATDynamics has taken care of the issue in the manner NHTSA recommended.

The FHWA will post this letter to their Commercial Motor Vehicle Size and Weight Web site for reference by the trucking industry. We will provide this letter to the Commercial Vehicle Safety Alliance and the American Association of State and Highway Transportation Officials for their information and use and further dissemination to their roadside enforcement officials. We will also provide this letter to the Environmental Protection Agency to inform their SmartWay Program. You may consider providing this letter to individuals using the 'Trailer Tail' product for them to provide to law enforcement officials.

If you have questions or need any further assistance regarding this matter, do not hesitate to contact Michael Onder, Team Leader, Vehicle Size and Weight Team,, 202-366-2639 or John Nicholas of the Vehicle Size and Weight Team,, 202-366-2317.


/s/ Anthony T. Furst

Anthony T. Furst
Director, Office of Freight Management and Operations

Cheryl L. Bynum
SmartWay Transport Partnership
U.S. Environmental Protection Agency
Phone: 734-214-4844
Fax: 734-214-4906

Luke W. Loy
Vehicle & Roadside Operations Division, W64-237
Federal Motor Carrier Safety Administration
1200 New Jersey Ave., SE
Washington, DC 20590
Phone: 202-366-0676

Collin B. Mooney
Director, Enforcement Programs
Commercial Vehicle Safety Alliance
1101 17th Street, NW -- Suite 803
Washington, DC 20036

Tim Johnson
National Traffic Highway Safety Administration
1200 New Jersey Ave., SE
Washington, DC 20590
Phone: 202-366-5664


John Berg

Office of Operations