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technical director

For more information, please contact Oscar Franzese, Technical Director, at or (865) 946-1304.

Brake wear and performance test (bwpt)

brakePerformance-Based Brake Testers (PBBTs) are devices that can be used to evaluate the current braking capabilities of a vehicle through the measurement of brake forces developed as a vehicle engages in a braking event while on a PBBT device. The FMSCA passed legislation on February 5, 2003, allowing a PBBT that meets the FMCSA functional specifications to be used as an enforcement tool. Previously, citations could be written, although the test results could not be used to put a vehicle out-of-service (OOS). Failure to meet minimum braking efficiency as measured by a PBBT was added as an OOS criterion effective April 1, 2007. However, the few PBBT machines within the continental United States are used primarily for screening and conducting research.

In August of 2005, the FMCSA tasked ORNL to: (1) assist the Tennessee Department of Safety (TDOS) in the procurement and installation of a PBBT machine; (2) train and certify PBBT machine operators; and (3) layout the framework for a Brake Wear and Performance Test (BWPT) project using the PBBT machine installed at the Greene County Inspection Station (IS). This equipment is a roller dynamometer with the capability of measuring a vehicle’s rolling resistance, weight, and brake force. In a typical PBBT test, the vehicle’s tires are placed on and between the rollers which will start rolling the wheels as if the vehicle were traveling forward and will attain a rotational speed of approximately 2 mph. As the driver gradually depresses the brake, the PBBT measures the force exerted by the braking system on the axle under test. This data is sent directly to the PBBT desktop computer. This process is repeated for each axle until the entire vehicle has been tested. The overall result reported is the brake efficiency, the ratio of the total braking force to the gross vehicle weight.

As part of the training plan, ORNL and Tennessee Department of Safety (TDOS) arranged for the supplier of the PBBT machine to conduct operational training and operator certification for all ORNL and TDOS staff responsible for operating the machine.

ORNL drafted the Brake Wear and Performance Test (BWPT) Test Plan in September 2007 with the approach of testing eight CMVs from four vocations for a period of twelve to eighteen months. Each vehicle would receive new foundation brake components before the start of the BWPT Field Operational Test (FOT) and then receive a PBBT test on a monthly basis to determine if the vehicle's ability to stop degrades over time. Additionally, ORNL would look at wear as a function of mileage and explore induced ovality within a vehicle's brake drums or rotors, and the PBBT's ability to measure this induced ovality.

See Fact Sheet (PDF, 1MB) and Final Report (PDF, 9MB)