Industry Concerns
Through discussions with the CVSA Associates Advisory Committee, a list of concerns was developed. Through collaboration with volunteer fleets, and an additional one year “trial enforcement period” data collection effort, these concerns have been addressed.
The initial industry concerns were the accuracy and repeatability of the PBBTs. The accuracy was addressed through participation by a fleet representative and a representative of
ATA in performing a calibration of the roller dynamometer-type PBBTs in use in Wisconsin.
Calibration results sheets are included.
Repeatability was demonstrated at the same time through a series of 20 PBBT measurements of an in-service vehicle provided by Schneider International. The repeatability was found to be within six percent among all the tests (maximum to minimum), and within 3 percent of the mean, as shown in the included repeatability graph. This is better repeatability than one would typically achieve in a stopping distance test, or even from laboratory tests in a controlled environment.
As to the third concern, some industry representatives believed they would not know how to bring their vehicle’s braking capability to a passing level should it fail a roadside PBBT test. First, in response to an industry suggestion, a simplified universal PBBT data presentation format was developed by the PBBT User’s Working Group. This would direct the driver or mechanic to the problem area(s).
To determine what repairs might be required, data were collected by the States of Washington, Indiana and Wisconsin. For over 100 vehicles for which the Braking Force as a Percentage of Gross Combination Weight was below 43.5% (i.e. considered failing per FMCSR 393.52), a subsequent Level 1 inspection was conducted. Documentation was made of the actions taken such that the vehicle passed a subsequent PBBT retest, as shown in the included pie charts. Further, data from an additional 58 vehicles for which a retest was unavailable were compiled. Not surprisingly, the data showed a relatively small set of repairs, all of which are common defects.
The list developedfrom the data collection effort was also used to provide a method for vehicles to get back into service should a PBBT test be unavailable, due to end of shift, close of operation, or unavailability of a PBBT operator. This also addresses the liability concern of the enforcement community. This list can be found on the last page of the ASPEN section.
Calibration Photos
 Download Calibration Photos PDF - 1 page, 88K
Calibration Result Sheets
Download Calibration Records PDF - 6 pages, 792K
Calibration Repeatability Photographs and Test Result Graphs
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| Vehicle # 1 lining up for repeatability tests under dry conditions. |
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Steer Axle of vehicle # 1 during repeatability tests. |
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| Pressure transducer installed to monitor air pressure during tests. |
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Wetting down tires for wet versus dry PBBT tests. |
Results of Repeatability Tests Conducted on Kenosha, Wisconsin PBBTs
March 21, 2005
Data and statistics from repeatability tests conducted using an in-service, 5-axle tractor semitrailer. Results show less than six percent maximum to minimum deviation, and less than three percent difference from the average.
Graphical depiction of the above data, showing excellent repeatability of PBBT results for a single vehicle on two different testers.
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