"Everybody talks about the weather, but nobody does anything about it." This throwaway remark more than a century ago by the American writer Charles Dudley Warner was pithy enough to ensure its immortality. But our National Roads Authority, or NRA for short, is out to prove Charles Dudley wrong. Earlier this month, in co-operation with Met Eireann, it inaugurated ICECAST, a state-of-the-art response to winter's icy roads.
Icy patches on a roadway can be disruptive to traffic, even lethal, so the authorities try to alleviate the situation by spreading grit or salt on the more important routes in dangerous conditions. A simple solution, but an expensive one to implement. There are ways, however, by which the benefits are maximised.
Some stretches of road are more prone than others to frost and ice in cold conditions. One place, for example, may be sheltered by trees, and therefore less vulnerable in this respect than another segment of road that lies in a hollow into which the cold air drains on a clear night.
It therefore happens that in marginal conditions, on nights when the temperature is not too far from zero, the entire network may not require treatment. The key to successful selectivity lies in thermal mapping, a process which identifies those sectors of a road network that are likely to remain relatively warm, or cold, in a potentially icy situation.
The technique involves a number of surveys of the network, in a variety of weather conditions, using a vehicle equipped with an infra-red sensor to provide a recording of the variations of temperature on the road surfaces along the different routes.
Armed with a thermal map, a number of automatic weather stations at strategic points along the route, and accurate forecasts of expected temperatures, it is possible to estimate the likely minimum temperature everywhere on a road network: the thermal map indicates the extent to which each point is likely to be warmer or colder than the key locations.
Corrective or preventive measures can then be concentrated on those stretches where they are most needed and where they will be most effective.
ICECAST is a computerised modelling package widely used throughout Europe in countries such as Switzerland, Germany and Austria that habitually experience severe winter conditions. In addition the NRA has invested £2 million to date on thermally mapping some 3,000 km of our national roads and installing automatic weather stations at strategic points.
A further £1 million will be spent to bring the entire network of national primary roads, and some of the more heavily used secondary roads, within the system before the end of 1999.