One of the biggest errors when calculating roughness, rutting and texture depth is the transverse position of the vehicle in the lane.
Even when the position of the vehicle along the road (with respect to chainage) has been correctly aligned, it is impossible to accurately control the position of the vehicle within the lane.
With a typical driver having errors of around +/- 250mm, small errors in horizontal positioning can cause large errors in the road performance measures.
To correct the road surface performance measures requires not only high accuracy positioning, but also high density data. For example a standard 13 point laser system may not have the data spacing to allow resampling of these measurements to facilitate more accurate recalculation of rutting, roughness or texture depth.
However, the high density 2048 point laser profiling unit within the PaveScout system has the data density to allow the adjustment of laser profile positioning to correct for lane positioning errors. The result is a vast improvement in the repeatability of the measurements between years. For example the graph below shows the difference in the data before and after RoadLock correction. In this data set, through the use of the RoadLock technology, we improve the coefficient of determination from 0.87 to 0.997, at a standard deviation error of 0.1mm. This exceeds the AusRoads standard. This can be achieved for any road in the network. The result is data where you know if a change has occurred, instead of guessing if a change has occurred.
To accurately classify positioning systems, RPS has defined a five class rating for vehicle based systems and the PaveScout (through the use of our RoadLock technology) is the only Class 1 road asset collection system.
|Positioning System Class||Chainage Error||Lane Position Error||Comments|
|Class 5||> 10m||> 0.1m||Relies on driver triggered feature points with a gradually increasing positional error due to encoder drift with wheel circumference errors (temperature and curves). This is the minimum standard as required by AustRoads.|
|Class 4||> 2m and < 10m||> 0.1m||Utilises GPS positioned features, rather than driver triggered features to increase chainage accuracy.|
|Class 3||< 2m||> 0.1m||Utilises corrected GPS, as opposed to non-corrected GPS, but does not attempt to align the vehicle within the lane|
|Class 2||< 1m||> 0.1m||Utilises correction GPR, linked to a high quality inertial unit to allow elimination of localised GPS errors.|
|Class 1||< 1m||< 0.1m||Utilises either centimetre accuracy GPS (reference station), or corrected GPS with an image based lane positioning system.|