Network Management – Asset Management (Pavements)

The Authority is responsible for the maintenance and development of a diverse set of road assets that includes the most fundamental element – the road pavement. Our network pavements are not uniform, the National pavement network consists of over 5,300 centreline kilometres of road. There are 33 National Primary routes and 32 National Secondary routes. Our road pavements are predominately made of layers of flexible materials that are designed to be strong enough to support the loads over their lifespan (c. 20-40 years). In addition, the surface course must also provide adequate wet skidding resistance, acceptable ride quality, generate acceptable noise levels and resist deterioration induced by environmental conditions.

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 may have evolved from historic routes that are often constrained by physical or environmental conditions.

We have built or inherited a network of c. 5400km of roads but like any asset they deteriorate with use.

• Road networks are one of the most important economic activities in modern industrialized societies and constitute an enormous investment of public funds
• To protect this investment, large sum of money are required to sustain and maintain the networks in an adequate condition
• The task is becoming more complicated by the limited of funds combined with the continuously deterioration of pavement structures over time due to environmental factors and increasing traffic loads

This scenario has focused agencies to look for better procedures or strategies for maintenance and rehabilitation of the existing pavements. All pavements over time deteriorate as a result of repeated loading from traffic and also by exposure to fluctuations in temperature and moisture content. As they deteriorate, they exhibit a number of fatigue (structural) and functional distress symptoms that are measured as part of an annual condition rating survey. These include:

•The development of wheel track rutting

•Increasing roughness

•Cracking

•Loss of skidding resistance

Following asset management principles, and through the use of a fully functional Pavement Management System, the onset and development of these symptoms is modelled utilising algorithmic relationships that predict the rate of deterioration.

Pavement Maintenance of the road network is undertaken with the following primary objectives:

1. To ensure that on a day-to-day basis the network is kept in a satisfactory operational manner.
2. To ensure that delays and disruption to road users are kept to a minimum through effective network management.
3. To ensure that the asset value of the network is not allowed to degrade. In order to achieve this, annual and multi-annual rehabilitation regimes are required in order to ensure that as the network condition is subjected to the accumulated actions of environment, weather and traffic, the infrastructure is maintained and renewed in a timely and prioritised manner.

As part of the Authority’s pavement management procedures, an annual survey of network pavement is undertaken of all national road pavements, utilising an array of electronic, laser and digital video equipment mounted on specialised vehicles. Year on year these surveys measure and record a range of network condition parameters including longitudinal profile / roughness, degree of rutting and skid resistance measurement. The data from these machine based surveys which are geo-referenced is recorded within the Pavement Management System. The data bank can therefore be used to accurately record the measured condition and compare it to previous surveys at that location. Together with recorded traffic volumes the rate of deterioration can be projected to enable a prioritisation of maintenance interventions programmes be established based on best practice asset management principles.

Both of the above schematic deterioration curves reflect not only that the pavement deteriorates with time but also continues to deteriorate even after an intervention of any scale.

Using the data gathered from the surveys the Pavement Management System incorporates software specifically designed to use it in analysis and prediction tools for current and future condition and remaining life time prediction. Also included are modules to assist in evaluating whole life cost analysis for maintenance and construction, deterioration models, assessment of value of the asset, risk based analysis, and prioritisation according to strategies and available budgets. In essence the PMS translates condition data into management information.

The more robust the intervention,  the higher the cost and consequently the PMS uses Life Cycle Cost Analysis to best determine how, where and when to renew the pavement to optimise the budget available.