Forestry is located in the parts of the country with the longest lengths of minor roads and relatively low-volumes of traffic. Such roads tend to be low on the list of council priorities for maintenance and strengthening. The last significant improvement of much of the minor road network was in the early twentieth century when the councils ‘adopted’ the local roads and gave them a coat of tarmac. The minor road network has largely served the minimal demands of a declining rural population, but the condition of these roads is now deteriorating and there is a serious backlog in maintenance.
Timber output in Great Britain has increased five-fold since the 1970s with many new areas of forest coming on stream. Modern harvesting machines can produce more than eight lorry loads of logs each day. The lorries are bigger too, increasing from 32 tonnes to 44 tonnes gross weight (though axle weights have not changed substantially).
Where a minor road crosses a stretch of soft ground or fill the road will flex with the weight of the lorry. The road should recover from occasional heavy traffic but repeated loading can damage the surface and the underlying layers.
On single track roads the lorry may be as wide as the carriageway placing the wheels at the weaker edges of the road. Long trailers can over-run tight corners causing damage to road edges and rear axles may scrub the road surface on tight bends. Passing places are limited and often too small to allow vehicles to pass without damaging verges and roadside drains. Poor roadside drainage further weakens the road structure.