High Friction Surfacing

High friction surfacing is the formal name for what most people call anti skid. It is a resin binder laid onto the running surface and dressed with a hard, angular aggregate, and its whole job is to give a tyre something to grip on the few metres of road where stopping distance actually decides the outcome.

HFS is not laid by the mile. It goes where braking and turning forces concentrate: approaches to signalised junctions and roundabouts, pedestrian and school crossings, approaches to bends, steep gradients over lengths greater than 50 metres, and the approaches to level crossings. It is the approach that is treated: the design standard is explicit that high friction surfacing must not be laid on the circulatory carriageway of a roundabout, and it must not be specified simply because a coloured surface is wanted. Highway authorities specify it against recorded skid resistance deficiency or collision history, which is why the extent of a scheme is usually decided before a contractor is anywhere near it.

The binder is a resin, hot applied or cold applied. The aggregate that does the actual work is normally calcined bauxite, a manufactured aggregate chosen because it holds a polished stone value of 70 or above, meaning it resists the polishing action of tyres far longer than natural stone. There is no lower-grade system at PSV 65, despite the figure being widely quoted. 65 is a minimum skid resistance value measured with a pendulum, and it applies to every system type equally rather than describing a second class of aggregate.

In the Specification for Highway Works this sits under Clause 924, High Friction Surfaces. Systems in highway use must hold a current HAPAS certificate or equivalent product acceptance scheme certification, and that certification requires installation by an approved installer, so the certificate and the installer are two separate checks a specifier should make rather than one. The RSTA and ADEPT Code of Practice for High Friction Surfacing is the practical reference for how it should be laid.

Certified systems are classified by type, with an expected service life of five to ten years at the maximum traffic level each type is rated for. The spread inside that range is almost entirely workmanship and weather. The surface has to be sound, clean and genuinely dry, above the minimum application temperature, and the aggregate has to be applied to full refusal while the binder is still live. Laid onto a damp or cold surface, or dressed a few minutes too late, an HFS system will start shedding aggregate in its first winter, and shed aggregate is both a loss of friction and a windscreen risk.

Almost all of it is night work under Chapter 8 traffic management, because the material needs a closed lane and time to cure before it takes traffic. We plan around the forecast as tightly as around the closure, and we would rather move a date than lay resin onto a surface that is not dry. Existing failed HFS is removed rather than overlaid.

We are based at Little Westerhill Farm near Maidstone in Kent. Kent, London, Sussex, Essex and the wider South East are covered from our own yard, and longer programmes are mobilised UK wide. HFS sits within our anti skid surfacing service, and most often runs alongside line marking on the same closure, since a treated approach usually needs its markings reinstating afterwards.