PSRV anti-slip and anti-skid resistance

Anti-slip is a pavement surface’s resistance to slipping commonly associated with Pedestrian traffic, whereas, Anti-skid is a pavement (or road) surface’s resistance to inducing vehicle skid.

Highways England DMRB CD 534 defines minimum anti-skid values as; 45+ PSRV for low-skid-risk areas and 60+ PSRV for high-skid-risk areas, obtained using the WRc test method. Compliance with CD534 [vehicle] skid resistance requirements does not necessarily ensure an equivalent level of slip resistance for predominantly pedestrian-trafficked areas and so this latter requirement is often achieved by the supplementary application of an appropriate anti-slip coating, although such coatings can demonstrate limited durability in vehicular trafficked environments. Pedestrian area surfaces are measured by their Pendulum Test Values (PTV) where the UK HSE recommends a minimum Floor Test Value of 36 PTV when dry, wet or contaminated.

Tristar, Highway & Unite skid resistance values have been obtained using testing methods derived for carriageway class products (D400 & E600), where vehicles are the most prolific form of traffic. In these circumstances, the testing reveals that the skid resistance of Tristar, Highway and Unite brands significantly exceed Highways England CD 534 skid risk requirements for High Skid Risk vehicular traffic areas (requiring 60 PSRV+).

However, whilst the macro texture of raised chequer patterns on the above D400 & E600 products provides effective skid resistance with vehicular traffic, slip resistance requirements for pedestrian-dominant areas may require a slightly modified version of the raised chequer profile. This slip resistance improvement may also be effectively delivered using a high-friction anti-slip coating.

We all know from experience that vehicles don’t always skid evenly when traversing slippery surfaces. But on such surfaces, they may at any point in time be on the cusp of skidding. Indeed, at this point, vehicles are at their most vulnerable to changes in surface conditions which might induce a skid.

These conditions include, but are not limited to:

• Differential skid resistance (friction characteristics) between the cover top profile and its surrounding road surfacing.
• Lubrication of the contact surface by rainwater or contaminants which change the contact friction between tyres and the traversed surfaces. e.g. oil, wet leaves.
• Disruptive cover and/or frame surface edge geometries that have inherently low friction or induce the loss of grip due to unsympathetic alignment to the direction of vehicle travel.
• Thermal effects that change to friction characteristics of the components surfaces in contact. e.g. with variations in tyre elastomers.
• Change in the force applied by the vehicle tyres to the trafficked surface.
• Friction characteristics of the vehicle tyres and their propensity to change contact area with varying inflation pressures.

Of these factors, differential skid resistance between surfaces is arguably the most relevant when selecting a skid resistance requirement for manhole covers used in a particular road surface. In order to achieve accuracy in this aim, their selection should take into account validated skid resistance values obtained from testing at recognised national facilities.

Minimising the differential skid resistance between a manhole cover and its surrounding road surface is vital in reducing the likelihood of a vehicle skid. In support of this, it is also important to recognise that when selecting manhole covers for operation in a given road surface of known skid resistance, its own skid resistance should closely harmonise with that of the surrounding road surfacing. i.e. not be significantly different. e.g. 70 PSRV road surfaces should ideally have 70 PSRV manhole covers installed in them, not those of significantly higher or lower PSRV value.

In May 2022 CD 534 was updated to v0.1.0. It now stipulates only one type of test for covers with BS EN 124 compliant raised chequer. Previously, skid resistance requirements could be satisfied by compliant results from the application of a conventional pendulum test, which measured the resistance caused to a swinging ‘shoe’ by the cover surface. Whereas, the more recent WRc skid resistance test measures the resistance to sideways skid of a small tyre across a cover’s surface.

As CD 534 is a Technical Regulation, it is now mandatory to demonstrate compliance with the WRc test. All manhole covers with the Wrekin triangular or Unite chequer satisfy the requirements of CD 534. This means all Wrekin Highway and Unite ranges comply with the requirement.

Wrekin’s standard chequer pattern (as seen on our; Surface Boxes, Tristar, Highway, SafeSeal, and Hercules ranges) has been certified by the WRc laboratory as achieving in excess of 70+ PSRV. These tests were carried out in accordance with the procedure described in National Highways DMRB, CD 534 v0.1.0 (Former Vol 4, Part 5, HA104/09, sub-section 3.4). Similarly, Wrekin's Unite chequer pattern has also been certified by the WRc as achieving in excess of 70+ PSRV.