Irish National Road Network
In the absence of a widespread rail or water transport network, Ireland’s road network plays a vital role in the country’s economy. The road network consists of over 5,300 centreline kilometres of road.
Transport Infrastructure Ireland (TII) primary function is to secure the provision of a safe and efficient network of National roads. For this purpose, it has overall responsibility for the planning, supervision of construction, road network management and maintenance on National roads.
A large proportion of the road network consists of “legacy” roads that have evolved from historic routes that are often constrained by physical or environmental conditions. This diversity in road construction as well as varied traffic volumes, leads to significantly different deterioration and failure modes across the network. Constraints in the geometrical alignment also tend to alter how the route is driven.For example, the average inter-urban speed is lower for routes with tight radius bends.
To manage this diverse network effectively, it was decided to define a series of five subnetworks in dTIMS by grouping similar sections such that there is considerably less variation in pavement condition, traffic and construction type. This approach enabled the service levels set for the different subnetworks to take account of the differences in traffic levels, pavement type and foundation characteristics of each subnetwork. The approach recognises the necessity to adopt progressively lower performance levels on Subnetworks 1 to 4, as compared to Subnetwork 0 (the motorway / dual carriageway network). In effect it recognises the constraints and adopts a “fit for purpose” approach. The performance levels are also used at tactical and strategic level for management of the network.
There have been a number of innovative developments in the TII’s management of the national network of pavements since the implementation of dTIMS. A number of subnetworks have been defined, with significantly different characteristics, and different levels of service brackets and intervention levels. In turn, this has led to the development of a new system of M&R scheme selection, based on a combined Percentage Above Threshold approach for two or more performance parameters that accords very well with scheme selection based on expert engineering judgement at the local level.