Lucy Phillips of TRL reports on IRWIN, a project which aims to use an improved local winter index to assess present and future needs for winter maintenance.

Winter indexes enable comparisons to be made between winters and average conditions in varying climatic regions of a country or a continent. A fully developed winter index can be used for different applications such as:

• Identifying compensation for winter maintenance costs in particular contract areas;

• Informing planning decisions, since historical and scenario data can be used to provide general needs in an area of varying size.

Winter indices have historically been calculated based on ordinary meteorological data which tends to have a poor spatial resolution. The technique developed by IRWIN uses the much more accurate spatial data from field stations in the Road Weather Information systems (RWIS) installed in most northern hemisphere countries.

This improves the accuracy of the index as a result of the density of the data (provided that a sufficient number of RWIS stations has been installed); the short time interval between weather recordings and the proximity of the RWIS stations to the road. The IRWIN index has also been linked to climate change scenarios meaning that it provides a useful tool to project expected changes in future maintenance needs.

The output of the IRWIN project is a more accurate local winter index which improves the reliability in estimating present and future needs for winter maintenance as well as their associated costs.


The technique developed by IRWIN to explore the likely impact of climate change on the road network uses downscaled climate data from Global Circulation Models and the historical road weather from field stations in the Road Weather Information systems (RWIS). Weather classes were developed and for each future day, the roadweather was taken to be that which had occurred in the past, after matching each day as closely as possible to the historical data. As a result of this process a novel database of possible future road condition scenarios was created combining archived historical RWIS data with widely accepted climate change scenarios.

Maintenance activities from the regions of interest were also collected, to be used in the winter index calculations to help establish the costs of the future maintenance needs forecast.

Potential for application of the approach

IRWIN's local winter index is a useful tool for local governments, winter maintenance contractors and roads owners to plan their dayto- day and annual winter maintenance operations, to project future maintenance needs and to estimate resources that would be required, for instance, for snow removal and de-icing.

The output of IRWIN is not only a winter index, but also a methodology on how to integrate historical data, climate data andclimate scenarios to provide information on current and future maintenance needs. The methodology could also be applied to explore the maintenance implications of hot weather, heavy precipitation and flooding, with a different set of outputs from the RWIS.

The index can be implemented in countries where winter maintenance has historically been, or is becoming an issue that has to be dealt with. The winter index can be used as a planning and budgeting tool for preventative maintenance, maintenance scheduling and to assist the effective allocation of resources. It also provides better information on extreme events, such as heavy snowfall and strong winds, which may impact on the serviceability of the road network. It should be noted, however, that countries wishing to adopt the approach will need to have access to:

• Good quality RWIS data ideally available over a long interrupted time series. This necessitates the installation of a sufficient number of RWIS stations where these are not already available

• Historical maintenance data so that current and projected maintenance needs can be estimated by using climate analogues for maintenance actions.

If climate change is to be taken seriously, as it should, the measurement and archiving of all pertinent road weather informationshould become a priority. The archiving of RWIS data in a central database, similar to what is being done in other countries such as the USA should be strongly considered.