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, the approach to a bend with a poor accident record, steep descents, bus stops and bus lanes, and the approaches to level crossings. 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. Lower PSV systems, around 65, are used where the demand is lower: village gateways, hatched areas, speed roundels and cycleways.

In the Specification for Highway Works this sits under Clause 924, Skid Resistant Surfacing. Systems in highway use should hold BBA HAPAS certification, and the certificate normally 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.

A BBA study of in-service sites found the majority achieving at least five years, with hot applied systems averaging around eight and cold applied around twelve. The spread inside those averages 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.