Road shape (surface form)

Road surface form

As part of the development and implementation programme to support the introduction of SCANNER surveys on all local roads in England, this research investigated the potential for using measurements of the shape (longitudinal and transverse profiles), on their own or combined with other measurements, to indicate the condition and maintenance requirements of all types and classes of local road, from principal roads to minor unclassified roads. It builds on research on transverse profile conducted by TRL Limited in 2004, details of which are available here.

The current SCANNER survey machines collect a range of data about the shape (longitudinal and transverse profile) of roads. This research investigated how routine measurements of the shape of the road surface, perhaps combined with other measurements, could be used to indicate carriageway condition and the road safety performance of the road.

This research was carried out by TRL Ltd. The final project report is here. Shape (surface form) of Local Roads

User perception studies on local roads showed that the longitudinal profile wavelengths that caused most user discomfort are in the range 1m to 5m, whilst those in the range 5m to 10m have less effect and those greater than 10m have no effect at all. Both 3m and 10m variance correlate quite well with user opinion, provided the profile is recorded in both wheel tracks.S

The research also developed a method of identifying individual bumps that cause user discomfort, based on the central difference method.

The report recommended that SCANNER should use a new definition for longitudinal profile variance, the "enhanced" approach developed by the Highways Agency, rather than the current "moving average" approach.

The research compared the performance of two different systems for measuring longitudinal profile, the 'GM' method and the "HRM" method and concluded that both have some advantages and some limitations, so that there would be no benefit from specifying one method or the other.

These results have been implemented in the SCANNER User Guide and Specification for 2007.

The research also investigated the practicality of combining longitudinal and transverse profiles to measure the road surface profile in three dimensions. It demonstrated that this is entirely feasible with current technology, but the 3-D surface profile needs to be combined with other measurements to provide useful information for road maintenance decisions.