Geometric inspection of raised traffic calming devices on public highways: road humps

Raised traffic calming devices (road humps) which are meant to reduce the speed of traffic on public highways to a maximum of 30 km/h have to meet the siting conditions and technical specifications laid down in the royal decree of 3rd May 2002, which has amended a previous royal decree of 9th October 1998. The changes introduced by the new decree consist mainly of tolerances in dimensions.

The reference for round-top road humps is still a hump with a length of 4.80 m, a maximum height of 12 cm and a sinusoidal longitudinal profile. The new geometric specifications for flat-top road humps distinguish at least ten different types by shape of on- and off-ramps (trapezoidal or sinusoidal), length of on- and off-ramps, and platform length (10, 12 or 15 cm, depending on local conditions). The combinations between the different platform lengths and the different ramp lengths are conditioned by the composition of traffic (with or without buses and/or many heavy goods vehicles).

Existing humps that fail to meet these requirements have to be removed or adapted during the redevelopment of the road (depending on prevailing conditions). To enable road managers to make a well-advised decision in this respect, a geometric inspection is necessary. In collaboration with the Belgian Federal Public Service Mobility and Transport (FPS-MT), BRRC has developed an original method (Méthode de Mesure CRR MF 77/06) of measurement in which all the relevant geometric aspects of a raised traffic calming device are checked for compliance with the legal requirements:

  • siting;
  • longitudinal profile of the on- and off-ramps;
  • combined gradient of the road and the on- or off-ramp;
  • length of the platform of a flat-top road hump;
  • marking of the on- and off-ramps, and evenness of the road pavement.

The method of measurement is mainly used to inspect existing road humps, the layout plans of which are most often not (or no longer) available, for compliance with the specifications of the decrees. It can also be implemented as an acceptance test for newly constructed road humps, when there is doubt about the conformity of the structure as originally designed.