Driving the decisions on which roads get repaired
* IRELAND has almost 100,000km of roads, of which 5,500km are national routes, making up the primary network. The primary network carries more than half of all traffic.
* The primary network is surveyed over a two-year period by Road Surface Profilers, vehicles equipped with electronic, laser and digital video equipment, which identifies cracks that cannot be seen by the naked eye.
* The machines look for wheel track rutting, caused by constant traffic, increasing roughness, cracking and loss of skidding resistance.
* The road is driven in one direction in year one, and in the opposing direction in year two, which allows engineers to determine its condition over time.
* Computer models are used to forecast deterioration, taking into account traffic volumes and extreme weather conditions. A decision can then be made on whether a road must be immediately repaired, or if works can be delayed.
* Road pavements are predominantly made of layers of flexible materials that are designed to be strong enough to support the loads over their 20- to 40-year lifespan. The surface must also provide adequate wet skidding resistance, acceptable ride quality, generate acceptable noise levels and resist deterioration caused by environmental conditions.
* Roads require large sums of money to sustain and maintain, and the task is becoming "more complicated" by the limited availability of funds, combined with the continuous deterioration of pavements over time, the NRA says.