Pavement slips

Introduction

The slip resistance of the road surface (also as a negative property called by the English literature as surface slip resistance) or (low skid resistance due to insufficient road friction) is the technical term to indicate the loss of traction on the wheels of vehicles due to the effects produced by the cumulative phenomena of snow, ice, water, loose material and texture of the road surface.[1].

Skid resistance can be measured as the friction between a free wheel and the ground, or the braking distance of a vehicle with the brake applied, and is directly influenced by the coefficient of friction between the wheel and the road surface.

Public road maintenance and conservation agencies spend a large part of the budget to improve the skid resistance of roads. Small increases in the slip resistance of a section of road can greatly increase accidents[2] Activities that affect slip resistance include repairing drains, snow removal, and road sweeping and cleaning. More intensive measures include brushing and grinding the pavements to give them a rough surface again, or if necessary, overlaying a new layer of asphalt.

A specific road safety problem can come from differences in the value of friction coefficient μ (mu). When friction differs significantly between the left and right side of the lane, the road may not be perceived as dangerous while accelerating, traveling at high speed, or even when braking gently. But in the event of sudden braking, the difference in friction can cause the vehicle to begin to rotate towards the side with greater grip. In the case of trucks it can cause the scissor effect, and trucks with trailers can see the trailer move forward. The difference in braking may be caused by a recent repair that has changed the texture of a localized area of the road or a change in color (ice patches form sooner on new black asphalt than on old gray asphalt).

Extent

The two ways to measure road slipperiness are the friction test and the emergency braking test. Friction testing can use surface or portable friction testers and involves allowing a freely moving object, usually a wheel, to rotate against the surface. By measuring the resistance experienced by the wheel, the friction between the pavement and the wheel can be obtained.

Stopping distance testing involves emergency braking on a test vehicle by measuring the distance required to make the stop. This can be measured by braking marks left on the pavement or by the "chalk-to-gun" system in which the vehicle's brake is connected to a gun that releases a chalk mark at the beginning of braking. This has the advantage of measuring the entire stopping distance, while the markings only indicate the distance where the wheels became locked.

Pavement slips

Introduction

Extent

Reduction

The slipperiness of roads can contribute to road accidents. In 1997 a study showed that more than 53,000 accidents were caused by slipping on roads in the United Kingdom (1.3% of the total). A small change in track slippage has a drastic effect on surface friction: reductions in the friction coefficient from 0.45 to 0.35; equivalent to covering the pavement with wet powder snow, increasing the accident rate by almost 1000%. Given this, road maintenance agencies have some techniques to reduce road slippage. Most roads are designed with camber, that is, with convex banking to reduce accumulated rainwater. In areas of the route where the slope is less than 0.5% (such as approaches to contracurves) the water will not drain well from the road. Storm drains should be installed at regular distances and modern pavement designs are designed to provide high friction in most conditions. The new permeable pavements are capable of absorbing all the water they receive, which makes them suitable for areas of intense rain.

Slippage on roads can be prevented or delayed by appropriate road surface design. The aggregate used in the pavement would have to be selected carefully, aggregates such as dolomite can be polished or smoothed due to tire wear. With asphalt pavements and surface treatments, using too much asphalt or asphalt emulsion can cause bleeding or flushing, a condition where excess asphalt rises to the top and fills the road texture. Both increase the problem of slippage, especially when the pavement is wet.

Once lost, the texture of the pavement can be restored with brushing and polishing procedures, and in some cases re-laying an additional layer of pavement.

The removal of ice and snow reduces the slipperiness of the road. Snow plows can remove snow while trucks that salt sandy roads provide greater grip on the surface. However, in dry environments the same sand and salt can increase the slipperiness of the road, so it will be advisable to clean it at the end of winter, something common in cities where road cleaning is carried out.

Reduction

Once lost, the texture of the pavement can be restored with brushing and polishing procedures, and in some cases re-laying an additional layer of pavement.

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Pavement slips

Introduction

Extent

Pavement slips

Introduction

Extent

Reduction

References

Reduction

References