Winter days with temperatures around zero degrees Celsius and enough snow to warrant ploughing entail several problems: lower average speeds, a higher accident risk and increased expenses for the road manager. In addition to ploughing, a considerable amount of salt is used to maintain a dry carriageway on major roads after a snowfall. This report defines a basic matrix with nine different weather situations classified according to temperature, air humidity and melted precipitation. This matrix was used to present the number of days of each weather situation, the traffic volume, average speed for cars and lorries with trailers respectively, and the salt used on the E20 European Highway outside Mariestad in mid-western Sweden. This matrix was also used to present accident statistics from seven counties in central Sweden. Between 1 October 1995 and 31 March 1996, there were 13 days with temperatures around or below zero and more than 2 mm of melted precipitation. The following observations were made: (1) 5-10 percent less traffic than during winter days with better weather; (2) 400 kg salt/km was used on roads of second highest maintenance priority; (3) the average speed for cars on the E20 was 86-92 km/h, which is 2-8 km/h lower than under favourable conditions; (4) the number of accidents resulting in death or serious injury was about 2.7 per day, twice as many as during a good winter day; and (5) less serious accidents increased somewhat more. The first three snowfalls in November were studied extra carefully through looking at the number of accidents 4 days ahead of and 4 days after the snowfall. The same pattern was found repeatedly, with the maximum number of accidents occurring on the day of the snowfall. Many of the additional accidents on that particular day occur on loose snow or slush, which is common when roads are salted while it is snowing. An average speed of about 89 km/h in the summer had been measured at the same point. This speed is partially due to the highway being relatively narrow and intermittently congested. The results indicate a high transport standard on the E20 in winter. However, when there is snow on the road, the speed is sufficiently high so as to pose a serious threat to road safety.