Understanding Your PSV/ HGV Roller Brake Test (RBT) Report: A Training Guide for Transport Managers & Operators

Introduction

As a Transport Manager for a PSV operation, ensuring the safety and roadworthiness of your fleet is paramount. Brake performance is a critical safety aspect, and understanding brake test reports is essential for effective maintenance and compliance. This training document will equip you with the knowledge to interpret Roller Brake Test (RBT) reports and understand their significance.

1. What is a Roller Brake Test (RBT)?

A Roller Brake Test (RBT) is a sophisticated method used to assess the braking performance of a vehicle. For PSVs, it's a vital procedure that measures the braking force of each individual wheel while the vehicle remains stationary on a set of rollers.

How it works:

1. Vehicle Positioning: The PSV is driven onto the RBT machine, with each axle positioned sequentially on rotating rollers.
2. Wheel Rotation: The rollers spin the wheels at a controlled speed, simulating road conditions.
3. Brake Application: The brakes (service, secondary, and parking) are applied gradually.
4. Force Measurement: Sensors within the RBT measure the braking force (typically in kilogram-force, kgf) generated by each wheel as it resists the rotation of the rollers.
5. Data Collection: The system records various parameters, including braking force, imbalance, binding, and lock-up, generating a detailed report.

Key Advantages of RBT:

• Individual Wheel Performance: Unlike other methods, RBT assesses each wheel independently, revealing specific issues like imbalances or binding brakes.
• Controlled Environment: The test is conducted in a controlled environment, ensuring repeatable and consistent results, regardless of weather or road conditions.
• Comprehensive Data: RBT provides detailed data on various brake system parameters, allowing for precise diagnosis of issues.
• Laden Testing (Ideally): For accurate results, it's strongly advised that PSVs are tested in a laden condition (ideally \geq 65\% of axle design weight). This ensures the brakes are tested under realistic operating conditions, as performance can differ significantly between laden and unladen states.

2. RBT vs. Decelerometer Brake Test

While both methods assess brake performance, they differ significantly in their approach and the information they provide.

In summary, while a decelerometer can give a quick overview of overall braking efficiency, the RBT provides a far more detailed and accurate picture of your PSV's braking system, allowing for proactive maintenance and better safety.

3. Understanding Your PSV Roller Brake Test Report

A typical RBT report for a PSV will generally be divided into three key sections:

Section 1: Vehicle and Test Details

This section provides general information about the vehicle tested and the test itself.

• Vehicle Registration/ID: Identifies the specific PSV.
• Make and Model: Basic vehicle identification.
• Test Date and Time: When the test was conducted.
• Test Centre Details: Where the test was performed.
• Gross Vehicle Weight (GVW): The maximum permitted operating weight of the vehicle.
• Design Axle Weights: The maximum design weight for each individual axle. This is crucial as brake efficiency is calculated against these weights.
• Measured Axle Weights: The actual weight on each axle at the time of the test. Ideally, this should be \geq 65\% of the design axle weight for laden tests. If unladen, there should be a documented reason/risk assessment.
• DTP Number: (Department for Transport number) A unique number for the brake test, often found on previous MOT printouts for PSVs.

Section 2: Brake Performance by Axle

This is the core of the report, detailing the performance of each brake on each axle. The report will typically show data for the Nearside (N/S) and Offside (O/S) wheels of each axle.

Key terms and what they mean:

• Axle Number: Identifies which axle is being tested (e.g., Axle 1 - Front, Axle 2 - Drive, Axle 3 - Rear Steer).
• Max Force (kgf): This is the maximum braking force achieved by each individual wheel during the test.

• Interpretation: A higher force indicates stronger braking. This figure is crucial for calculating overall efficiency and identifying imbalances.
• Failure Point: If the maximum force recorded is less than 5% of the measured axle weight for a wheel, it indicates a significant issue and will likely result in a failure.

• Imbalance (%): This is the percentage difference in braking force between the nearside and offside wheels on the same axle.

• Calculation: Typically, it's the difference between the higher and lower braking force, divided by the higher force, multiplied by 100.
• Interpretation: A high imbalance indicates that one brake on an axle is performing significantly better or worse than the other. This can lead to the vehicle pulling to one side under braking, compromising stability and safety.
• Failure Point: For service brakes and designated secondary brakes, an imbalance of more than 30% will result in a failure. Even if it passes, a significant imbalance (e.g., 20-29%) warrants investigation.

• Bind (%): This measures the residual braking force when the brakes are not applied. It indicates if a brake is sticking or "binding," causing drag.

• Interpretation: Any binding indicates resistance, leading to increased fuel consumption, excessive heat, and premature wear.
• Failure Point: More than 4% bind (on service brakes) will result in a failure.

• Time Lag: This assesses the time it takes for the brakes on an axle to apply and release simultaneously.

• Interpretation: Significant time lag can indicate issues with the air system (for air brakes) or the hydraulic system. It can also contribute to vehicle instability.
• Failure Point: This is often a manual assessment by the tester.

• Ovality (%): This refers to the variation in braking force during a single rotation of the wheel. It can indicate a warped or out-of-round brake drum or disc.

• Interpretation: High ovality can cause brake judder or pulsation, leading to discomfort and reduced braking effectiveness.
• Failure Point: 70% or higher ovality will typically result in a failure (more common for HGVs, but relevant for PSV front axles).

• Lock-up Detection: The report may indicate if a wheel locked during the test (often shown with an "(L)" next to the force figure).

• Interpretation: While a pass can still be recorded if a wheel locks (especially on unladen vehicles), it indicates that the maximum potential braking force may not have been achieved or that the wheel locked prematurely. This is why laden testing is so important.

Section 3: Test Summary and Efficiencies

This section provides an overall summary of the brake performance for all braking systems.

• Total Measured Vehicle Weight: The sum of all measured axle weights during the test.
• Required Efficiency (%): The minimum braking efficiency mandated by DVSA for each brake system (Service, Secondary, Parking).

• Service Brake: Minimum 50% efficiency.
• Secondary Brake: Minimum 25% efficiency (if independent of service brake). If the split service brake system is designated as the secondary, its performance is not separately assessed here.
• Parking Brake: Minimum 16% efficiency (against Design Gross Vehicle Weight or Design Gross Train Weight, whichever is higher).

• Achieved Efficiency (%): The actual braking efficiency achieved by the PSV for each brake system during the test.

• Calculation (simplified): (Total Maximum Braking Force of all wheels / Total Measured Vehicle Weight) x 100.
• Interpretation: This is the headline "pass/fail" figure.

• Overall Pass/Fail Outcome: Clearly states whether the vehicle passed or failed the brake test.

Important Note on PSVs: Unlike HGVs, PSVs do not have a plating certificate for Gross Vehicle Weight (GVW) in the same way. The DTP number from the previous MOT printout is crucial for ensuring consistency in testing standards.

4. Interpreting the Report and Taking Action

Simply seeing "PASS" on a report is not enough. As a Transport Manager, you need to dig deeper.

Questions to ask when reviewing a report:

• Overall Pass/Fail: Did the vehicle pass? If not, what were the specific failure points (e.g., efficiency, imbalance, bind)?
• Efficiency Values: Are the achieved efficiencies for Service, Secondary, and Parking brakes comfortably above the minimum required? Being just above the minimum could indicate underlying issues.
• Imbalances: Are there any high imbalances (even if they "pass") that suggest an issue with a specific brake? A 25% imbalance, though a pass, indicates one side is doing significantly less work and requires investigation.
• Bind: Is there any evidence of binding? This means wasted fuel and excessive wear.
• Max Force: Are the individual wheel forces consistent across an axle and between axles? A significantly lower force on one wheel points to a problem.
• Laden Test Confirmation: Was the test conducted laden (for PSVs, ideally \geq 65\% of axle design weight)? If not, is there a valid documented reason (risk assessment) for an unladen test? An unladen "pass on locks" below the minimum efficiency might not reflect true laden performance.
• Trend Analysis: Compare current reports with previous ones for the same vehicle. Are there any trends indicating a decline in performance? Are imbalances increasing over time? This proactive approach can prevent breakdowns and failures.
• Compared to Sister Vehicles: How does this PSV's brake performance compare to similar vehicles in your fleet? Significant differences could highlight a specific vehicle issue or a maintenance practice discrepancy.

Actionable Steps for the Transport Manager:

1. File the Report: The RBT report is a vital legal document. File it securely as part of the vehicle's maintenance records.
2. Investigate "Near Misses" / Advisories: Don't just focus on failures. A passing report with high imbalances or indications of binding needs immediate investigation and corrective action.
3. Schedule Repairs: If any defects or concerning trends are identified, arrange for prompt investigation and repair by competent technicians.
4. Document Repairs: Crucially, document all investigations, repairs, and parts replaced. This forms an audit trail for compliance.
5. Re-test as Necessary: After significant brake repairs, consider a re-test to confirm the effectiveness of the work.
6. Communicate with Technicians: Use the RBT report as a diagnostic tool. Discuss the findings with your maintenance team to target specific issues.
7. Review Maintenance Procedures: If recurrent issues appear across the fleet, review your preventative maintenance schedule and procedures.

Conclusion

Understanding the Roller Brake Test report is an indispensable skill for any PSV Transport Manager. It goes beyond a simple pass or fail, offering a detailed snapshot of your vehicle's braking health. By proactively interpreting these reports and taking appropriate action, you can significantly enhance the safety of your fleet, ensure compliance with DVSA regulations, and contribute to the longevity of your vehicles.