Longitudinal profile analyser (“Analyseur de profil en long”, or APL) – measurement of the longitudinal evenness of roads

The Belgian Road Research Centre has a longitudinal profile analyser for continuous measurements of the road profile. The measured data can be used to quantify the longitudinal evenness of a road and to calculate inticators such as the coefficient of evenness (CP, which stands for coefficient de planéité in French) and the international roughness index (IRI). Longitudinal evenness is an important factor for the safety and comfort of road users. The high accuracy of measurement makes the APL also suitable for research purposes. The measuring wheel bumps up and down with the relief of the road. This movement causes a change in the angle formed by the wheel-bearing arm in its hinge point. An inert pendulum in the bearing arm transforms the road profile into an electric signal. The angle between the bearing arm and the pendulum is recorded every 5 cm. This allows a graphic representation of the “pseudo-profile” of the road surface. A constant survey speed of 21.6 km/h, 54 km/h or 72 km/h is required.


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