Relative displacement or response-type devices

The relative displacement or response-type devices were the first to be introduced for measuring surface evenness at driving speed. These devices have a low purchase cost and are still in use in many countries. They measure the relative displacement of the measuring wheel, or of the vehicle s rear axle, and have the ability to rapidly record surface evenness since measurements are taken at 30 km/h or higher speeds. 

The roughness index determined by the TRRL bump integrator at a standard operating speed of 32 km/h, BI,.32, is the integrated vertical movements, in centimetres, divided by the distance travelled, in kilometres. The determination of BI,32 is usually carried every 1 km length interval other length intervals may also be used (0.25 or 0.5 km). 

When the test speed is other than 32 km/h and within the range of 20 to 65 km/h, the following conversion equations can be used (Jordan and Young 1980)  

To improve the accuracy of measurement on short sub-sections of a road, a microprocessor-based integrator unit has been developed and has replaced the mechanical integrator fitted to the trailer of the standard bump integrator. The new equipment enabled the unevenness index of sub-sections as short as 30 m to be measured with an accuracy of better than 3%. This accuracy on short sub-sections made the bump integrator suitable for use with the CHART highway maintenance system (Still et al. 1983). 

Other profilometric method. The calibration procedure is described, together with other operational information, in TRRL RR 301 (Cundill 1991), Mrawira and Haas (1996) and TRL Report 229 (Cundill 1996). Relevant information can also be found in TRL DFID (1999). 

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