Crazy roads?

This article was published in 2009, in Newsletter 84.

Have you noticed how so many roads have a surface that many would envy for their crazy paving?

I’ve observed this increasing over the years, and following this winter, an epidemic has occurred.

Crazing in Downing Street
Image as described adjacent

So what causes this? I’m sure it is the increasing volume of heavy traffic. Buses are larger, and there are more of them, and goods are delivered in increasingly larger vehicles. Once any cracks appear, water can get in and when that water then freezes in a winter such as we’ve had, damage escalates.

Technically the road structure is called the ‘pavement’ and excessive axle weights cause damage to the load-bearing structure below what is termed the ‘wearing course’. When this top level is worn or becomes polished and slippery it can relatively easily be replaced by ‘cold planing’ the top inch or so and replacing it with a good quality smooth surface. For cyclists this is often a huge improvement because the surface may be poor due to innumerable holes that have been dug to repair or replace services such as gas pipes and sewers, and not well re-instated.

My concern is not those repairs but the crazed cracks on the road surface. These cracks are the result of failures in lower layers often caused by increasing numbers of heavier vehicles.

Fixing such cracks by patching the surface is almost like putting a sticking plaster on an infected wound. Eventually the whole area will need to be dug out to a deeper depth and repaired.

Patches on patches: Fulbourn Old Drift
Image as described adjacent

Damaging power

The general rule for the ‘damaging power’ of an axle is related to the fourth power of the axle weight.

After those of a mathematical bent have picked themselves up from the floor, we need an explanation for ordinary mortals.

Such repairs will not come cheap, and although the taxation regime for lorries was modified some years ago to better take account of these factors, it is generally accepted that heavier vehicles do not pay for the damage they do to the road. So the next time a car driver tells you ‘You don’t pay road tax’ just tell them that it takes ten thousand bikes to damage the road as much as a single car!

Jim Chisholm