Skid-resistant road surfacing

The situation is complicated, however, because some of the drag on a skidding tire is due to the elastic hysteresis effect discussed in Section XII-2E. That is, asperities in the road surface produce a traveling depression in the tire with energy loss due to imperfect elasticity of the tire material. In fact, tires made of high-elastic hysteresis material will tend to show superior skid resistance and coefficient of friction. 

Traction zone or actual contact zone This region is the rear part of the contact area, beginning with the end of transition zone. It is the zone where most of the traction or skid resistance is developed. Here, the lubricating water him has been totally or substanhaUy removed, and vertical equilibrium of the tread elements on road surface has been attained. 

The friction of road surfaces is often measured with a skid tester developed by the Road Research Laboratory17 and this has also been widely used on other surfaces and floors, including artificial sports surfaces. It is a pendulum device, the movement of which is arrested by the foot of the pendulum skidding on the surface to be measured. The skid resistance indicated can be approximately related to coefficient of friction by ... 

The addition of thermoplastics to modify road surface compounds based on bitumen has been reported, the object being to improve the flexibility of the compounds and resistance to skids. 

Sand-asphalt-sulfur surface-wearing courses prepared with coarse sands have a sharp, sandpaper-like surface texture. Skid resistance tests carried out up to speeds of 50 mph have given favorable results. The road surface is not susceptible to polishing because as soon as a sand grain is worn away or dislodged, another sharp sand grain is exposed. Fine sands, such as dune sands, are not suitable for riding surfaces because they yield surfaces which are too smooth. 

Petroleum asphalt is used extensively as a binder in concrete road paving, hence road asphalt. Mixed with asphalt, coal tar pitch makes exceptional road surfaces that resist oils, are non-skid, adhere excellently to stone, and provide weathered hard surfaces. Cutback asphalt is asphalt dissolved in and made less viscous by a solvent (usually a petroleum distillate) allowing easier application in road repair and waterproofing. Road oil is very fluid asphalt used as a dust suppressant. 

The noise generated from moving vehicles on open-textured surfaces, similar to PA, has been found to be reduced when compared with conventional surfacing materials of the same macro-texture and skid resistance coefficient. The reduction measured was 3 to 4 dB(A), when the pavement surface was dry, and 7 to 8 dB(A), when the surface was wet (Nelson and Ross 1981). Similar results were also found by the Belgium Road Research Centre (Decoene 1989) and by Phillips et al. (1995). At a later study, resurfacing an old concrete pavement with PA led to wind-normalised reductions in noise exposure of the order of 4.5 to 6 dB(A) L/ io,i8h at villages approximately 0.5 km from the motorway (Baughan et al. 2002). 

The most objective assessment of functional pavement condition evaluation is conducted using purposely built devices that record the pavement s surface characteristics, in particular evenness, skid resistance and texture depth. These devices are self-mobile, mobile or portable when a short length of road pavement has to be surveyed. 

Figure 16.4 Terms and explanatory notes on surface texture. (Adapted from Sabey, B.E., The Road Surface Texture and the Change in Skidding Resistance with Speed. Ministry of Transport, Road Research Laboratory, Report LR 20. Harmondsworth [Crowthorne], UK Transport Research Laboratory, 1966.)...

Surface skid resistance is measured by self-powered mobile devices or towed mobile devices. Spot measurements or measurements over short road sections are usually carried out by the British pendulum or ether portable devices. 

The wet-road skid resistance is determined by the SFC known as SCRIM coefficient, SC. The result is expressed in two decimal points and it ranges, theoretically, from 0 to 1.00 units (the greater the value, the higher the skid resistance provided by the pavement surface). 

In order to assure road safety, countries have implemented intervention or threshold skid resistance limit values (levels) that, when reached, would require immediate action for surface skid resistance restoration. 

It should be said that when restoration of skid resistance is decided and until works begin, it is vital that the road authorities put appropriate warning sings regarding the low skid resistance provided by the pavement surface. 

CEN EN 13036-4. 2011. Road and airfield surface characteristics - Test methods - Part 4 Method for measurement of slip/skid resistance of a surface - The pendulum test. Brussels CEN. 

CEN/TS 13036-2. 2010. Road and airfield surface characteristics — Test methods. Part 2 Assessment of the skid resistance of a road pavement surface by the use of dynamic measuring systems. Brussels CEN. 

CEN/TS 15901-1. 2009. Road and airfield surface characteristics - Tart 1 Procedure for determining the skid resistance of a pavement surface using a device with longitudinal fixed slip ratio (LFCS) RoadSTAR. Brussels CEN. 

TYROSAFE (Tyre and Road Surface Optimisation for Skid Resistance and Further Effects). 2008. D04 Report on state-of-the-art of test methods. FEHRL, 7th Framework Programme, December. 

The skid resistance of the road surface has been shown to be an important safety factor, especially when the surface is wet. There is concern about the early-life skidding resistance of some surfacing materials. 

Designers may want to use traditional granite setts as a road surface while Road Safety Auditors want adequate skid-resistant surfaces to enable drivers to stop safely. 

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