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DRAFT⚠OIML SMART pilot programme · internal use only · all documents and specifications are drafts and may change without notice
OIML SMART

OIML R 129: Dynamic measurement of road vehicle mass

Weigh-in-motion (WIM) systems measure the mass of road vehicles as they drive over a sensor, used for enforcement, tolling, and infrastructure planning. R 129 defines the metrological requirements that make those measurements legally valid.

Scope

OIML R 129:2000 specifies requirements for automatic weighing instruments that dynamically determine the mass of road vehicles in motion. It covers:

  • Bridge and platform WIM systems.
  • Axle-load and full-vehicle measurement.
  • Accuracy classes: 0.2, 0.5, 1, 2, 5, 10.
  • Speed ranges, environmental conditions, vehicle classes.

What’s modelled

Layer Count
Requirements 35
Conformance tests 14
Forms 9
Terminology ~50

Headline tests

  • Vehicle total mass accuracy (R 129 §5.1), dynamic measurement of total vehicle mass vs static reference.
  • Single-axle load accuracy (R 129 §5.2), per-axle measurement within tolerance.
  • Axle-group load accuracy (R 129 §5.3), grouped axles (tandem, tridem) measured as a unit.
  • Speed effect (R 129 §5.4), measurement stability across the rated speed range.

The dynamic-vs-static comparison introduces additional computation: each test requires repeated runs at multiple speeds, with statistical aggregation (across runs and within speed bands) producing the final verdict.

Computation: dynamic error aggregation

A typical R 129 dynamic error form computes:

calculation: r129_dynamic_error
inputs:
  - measured_values     # list of dynamic readings
  - reference_value     # static weighing
  - tolerance_pct       # class-dependent tolerance
expression: |
  (max(measured_values) - reference_value) / reference_value * 100

The form then evaluates whether the computed error falls within the tolerance band for the WIM system’s accuracy class.

Explore the model

Certification path

Certification of WIM instruments follows the same workflow as other Recommendations, with one twist: field testing at an installed site is typically required for accuracy classes 0.2 and 0.5, since the WIM system’s accuracy depends on the pavement and sensor installation.