Scope
OIML R 91:2025 specifies requirements for traffic speed meters, the instruments that measure the speed of road vehicles for enforcement. It is published in four parts:
- R 91-1, metrological and technical requirements.
- R 91-2, test procedures.
- R 91-3, test report format.
- R 91-4, type evaluation report format.
The Recommendation covers stationary and moving modes of use, fixed and mobile installations, and the measuring principles on the road: Doppler radar, range-finding, average-speed (section control), fixed-distance, image-based, and across-road technologies. One speed meter may belong to several categories at once.
What’s modelled
| Layer | Count |
|---|---|
| Requirements | 57 |
| Conformance tests | 64 |
| Report forms | 78 |
| Terminology | ~70 |
The package ships as a preview edition (2025): the model is complete against the four parts, and the published text supersedes the preview when the committee’s final edition appears.
Headline tests
- Documentation and visual examination (R 91-1 §8.1), the type documentation, markings, sealing, and manual against the construction clauses.
- Vehicle identification certainty (R 91-1 §6.6), the measured speed cannot be attributed to the wrong vehicle, verified through scenario review and image-evidence checks.
- Speed linearity (R 91-1 §6.5), ±1 km/h up to and including 100 km/h, ±1 % above, with influence quantities minimized.
- Dynamic performance (R 91-2), the meter’s response against a moving target across the measuring interval.
- Field tests, moving-mode and ego-vehicle runs in real traffic, plus the moving-traffic simulation.
- Influence and disturbance battery, the climatic, mechanical, and electromagnetic compatibility set (dry heat, cold, damp heat, vibration, bursts, surges, RF fields, and the road-vehicle supply disturbances).
Computation: the MPE lookup
Traffic speed meters carry a two-regime MPE structure, and the moving mode splits further into accuracy classes:
- Stationary measurements (R 91-1 §6.4), ±3 km/h at speeds up to and including 100 km/h, ±3 % above.
- Moving measurements (R 91-1 §6.15.1), class A mirrors the stationary limits; class B widens to ±7 km/h and ±7 %. The OIML certificate indicates the class.
The model encodes the regime transition as a table lookup keyed on the reference speed and the declared metrological class:
limit {
expression "ocl{abs(speed_error) <= lookupMPE(reference_speed, metrological_class, 1.0)}"
relative_to reference_speed
uses { speed_error reference_speed metrological_class }
}Relative units bind to the absolute value of the reference speed, never to the device under test (R 91-1 §3.5.2 NOTE), and the reference value is never rounded to integer values (R 91-1 §6.3).
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Certification path
Certification of traffic speed meters follows the standard workflow. The field-test parts of the evaluation run on the road or against the moving-traffic simulation, and the type evaluation report follows the R 91-4 format the model carries as forms.