Performance-based brake testers (PBBTs) and liquid freight

Source: Performance-based brake testers (PBBTs) and liquid freight


If you run in one of the many states that have one of the devices shown above — a performance-based brake tester (PBBT) — it’s likely you’ve seen one in operation. I’ve written about them before in various contexts. I know Wisconsin, Georgia, Tennessee and Florida, among others, have one or more of the units in operation. The Commercial Vehicle Safety Alliance describes the devices, some of them installed permanently (such as at the I-81 SB scale in Greene County, Tenn.) and some (like the above in Georgia) mobile units capable of deploying anywhere, this way:

A Performance Based Brake Tester (PBBT) measures the slow speed brake force and weight at each wheel, adds up the total vehicle brake force, and divides it by the total vehicle weight to determine overall vehicle braking efficiency. U.S. federal regulations and the North American Standard Out-of-Service Criteria require a minimum braking efficiency of 43.5%. If your vehicle’s braking efficiency is below 43.5%, your brakes are in need of service because they are not providing the minimum stopping power required and are performing poorly.

If you cross a PBBT and the overall braking efficiency falls below the 43.5 percent measure, you can be put out of service, according to the CVSA out-of-service criteria. Applicable regulatory language is spelled out in 393.52. Some of the discussion around PBBTs at last week’s CVSA Workshop event in Chicago told me a few things you might keep an eye out for, now and in the future.

Issues measuring brakes in liquid bulk applications
If you haul liquid bulk, whether in a tanker or in totes, the difficulty of obtaining accurate weights at each wheel end given the sloshing of the liquid as individual axles move over the PBBT’s roller often produces errors in readings that, if not heeded by the inspector, can be compounded as the machine makes its overall braking force calculation.

The upshot: If you’re put out of service as a result of a PBBT measurement and the inspector clearly didn’t give adequate time for the liquid to totally settle, you may have grounds for a DataQs challenge to the violation via FMCSA’s system.

At once, most inspectors utilize the PBBT as another tool in the entire Level 1 inspection, which also includes measurements of push-rod travel, visual inspection of brakes and more. If they can’t get you one way, they may get you another.

PBBTs serve something of a screening function, too. Even if overall braking force is not sufficiently low to put you out of service, force readings at individual wheel ends will show a particular brake that has issues, if they exist. Officers can then move in the visual aspects of the inspections to focus in on that brake to check for problems. Operators receive print-outs with each PBBT measurement that show individual and overall measurements. Utilize the data there to focus maintenance checks down the line for brakes not performing like the remainder.

OOS criteria may drift beyond overall PBBT efficiency measurement
The future of PBBT use may well extend OOS criteria relative to the machines’ measurements of truck braking power beyond the overall efficiency threshold of 43.5 percent. When CVSA developed that OOS criteria, it also discussed the potential for establishing individual criteria for single wheel ends that were mentioned again as a topic for future discussion at the Workshop last week. We’ll update you should further discussion materialize.

Have you rolled across a PBBT? Share your experience in the comments here.