Roads on these islands at the end of the 18th century varied greatly according to the nature of the local soils. Many were impassable to carts and wagons after the first autumnal rains set in, and for fully half the year travel could be undertaken only on foot or horseback. With the coming of spring, the roads were levelled by means of "ploughs" drawn by a team of horses, after which normal traffic could resume ad interim.
John Louden McAdam introduced what we now see as normality. McAdam was born in 1756 in Ayr, Scotland, and having amassed a modest fortune as a young man in the American colonies he returned home to devote his life to his abiding interest - roads.
McAdam produced an engineering solution to the problem. After years of experimentation he proposed a raised surface of broken stones, each stone angular in shape and weighing no more than six ounces. The road would be consolidated into a firm, hard surface by the weight of the traffic passing over it and would be provided with drains on either side. His recipe was adopted almost universally for trunk routes throughout these islands, and a new word, "macadamised", was coined. With the advent of the motor car it became necessary to devise some means of keeping down the dust, and so a coating of tar was applied to the macadamised road, and tarmacadam had arrived.
Modern trunk roads are direct descendants of McAdam's surfaces, but their effectiveness is still dependent on the weather of the changing seasons, albeit in rather different ways. The three main hazards nowadays are ice, fog and strong crosswinds. Their effects can be minimised by meteorological surveys carried out when the roads are being designed and built: proposed stretches of highway likely to be particularly vulnerable to these hazards are identified in advance and sometimes a small diversion of the route may be sufficient to avoid the worst scenarios.
Once built, however, many trunk roads nowadays are provided with meteorological instrumentation to monitor potential hazards. In the case of fog, for example, roadside sensors may trigger illuminated signs when visibility falls below a predetermined value; anemometers along vulnerable stretches alert the authorities when certain wind-speeds are exceeded, so that temporary speed limits can be introduced, lanes closed, or movements of vehicles of particular kinds restricted; and temperature sensors on the road surfaces give warning of impending icy patches.
It would have pleased John Louden McAdam to see how his brainchild had developed. But of course, he did not live that long; he died 163 years ago yesterday on November 26th, 1836.