Recent Developments in Pavement Management on Irish National Roads
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The Irish National pavement network is Ireland’s strategic road network consisting of over 5,300 centreline kilometres of road and is managed by the National Roads Authority (NRA). There is a very significant variation across the network under a variety of headings, including pavement construction, pavement age, carriageway width, lane width, geometric design and traffic volumes carried. A large proportion of the 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, e.g. The average inter-urban speed is lower for routes with tight radius bends. Accordingly, a range of innovative measures have been adopted to customise and adapt the Authority’s Pavement Management System for the Irish National road system. The objective of this paper is to describe these innovative measures to an international audience. Pavement Condition data collection using high speed machine survey vehicles has been carried out annually on the National road network. Most of the road condition data is collected using the Road Surface Profiler (RSP) machine. The skidding resistance data is collected using the Sideways-force Routine Investigation Machine (SCRIM). In 2013, LCMS has been used to collect cracking and ravelling data on the entire network. In addition, in 2013, a Ground Penetrating Radar (GPR) survey has been carried out on the entire network to improve the pavement construction and layer thickness data. To manage this diverse network effectively, it was decided to define a series of five subnetworks 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 is a comprehensive managed skid resistance programme based on 100% measurement of the skid resistance of the network on an annual basis. Principles of risk equalisation have been developed with a range of skid resistance investigatory values used on the network, dependent on the road section characteristics – approaches to roundabouts and traffic lights having significantly higher skid resistance requirements than straight line nonevent sections, for example. This skid resistance policy is applied consistently across all subnetworks. The NRA corporate GIS, ArcGIS, is used to co-ordinate and cross-reference the data from a range of management systems including the PMS, Bridge Management System, Accident Database, Traffic modelling database, Routine Maintenance Management Systems among others. A new ArcGIS add-in has been developed for the NRA to allow display and querying of the imagery collected on the annual surveys.The processed video is also available to the NRA and its clients through a web browser system.