The large-scale winter model project resulted in a model for assessing the most important effects and the monetary value of changes to winter maintenance strategies and operations. The winter road condition model was the central part of the winter model. The road condition model characterized the state of a winter in terms of a road condition description hour by hour. The road condition model provided input data for the other models assessing different effects such as accident risk, travel time, fuel consumption, and environmental effects. In the first stage, a model that described how road conditions were affected by weather, what maintenance measures were taken, and the volume of traffic on two-lane rural roads with a width of 7 to 9 m and speed limit of 90 km/h was developed. To a great extent, the basis for developing the winter road condition model was data already collected from nine observation sites with the purpose of developing the accessibility model. For several periods data from these observation sites contained information hour by hour regarding weather, traffic flow, initial road condition, maintenance measures taken, and specified types of road condition development mainly connected with snow ploughing and anti-icing measures. Additional information, such as development of ruts down to the pavement in hard-packed snow or thick ice caused by vehicles with studded tires and conditions for a wet or moist road to dry out, was collected by field studies during the 2002-2003 winter season.