This publication reports on analyses into the relation between weather conditions on the one hand and bicycle use and numbers of cycling casualties on the other. The analyses reveal that the annual fluctuations in both bicycle use and number of cycling casualties may to a large extent be explained by weather conditions.

Conclusions on bicycle use:

• Bicycle use is mainly related to the annual number of warm days. In years with many summery days (max. temperature over 25 degrees centigrade) the average Dutchman cycles considerably more. The number of wet and cold days also has an impact, but less than the number of warm days.
• Young people on the other hand seem less affected by warm weather. They cycle noticeably more, on the other hand, when a year has fewer wet days.
• Bicycle use of the average Dutchman has increased by approximately 6 per cent over the past twenty years. This is mainly caused by the fact that since the turn of the century weather conditions have been more favourable.

The analyses have also revealed an error in the CBS data on bicycle use. The correction for trend change applied retroactively by CBS to the years up to and including 1998, has been insufficient. The data for bicycle use over that period have to be decreased by approximately 5 per cent to come into line with the new research methodology CBS has been applying since 1999. This correction may affect all trend analyses made over the past couple of years.

Conclusions about the number of cycling casualties:

• Weather conditions indirectly affect the number of cycling casualties per year. In a year with good weather conditions the Dutch cycle a lot more, thereby increasing chances of cycling accidents. The relation between weather conditions and the number of cycling casualties can be directly demonstrated.
• In warm years there is a specific increase in the number of elderly cyclists that are killed. The elderly cycle predominantly more in good weather. Elderly cyclists are moreover relatively vulnerable, as a result of which accidents are more often fatal.
• In years with few cold and wet days the number of hospitalisations particularly increases. This concerns both the young and the elderly.
• Apart from annual fluctuations in the number of cycling casualties due to the weather and bicycle use there is a strong downward trend in numbers of casualties. Over the past two decades on average 9 cycling fatalities and 69 hospitalisations have been recorded annually. This is partly the result of a deterioration in administrative practices, but there is a real decrease particularly in the numbers of fatalities.

In policies extra attention to the safety of elderly cyclists is warranted. Due to the ageing population the amount of kilometres cycled by the elderly is increasing anyway. Climate change may reinforce this trend. The elderly, too, want to take advantage of the increasing number of warm days and take to their bikes more often. This is positive for public health and social participation of the elderly. In traffic policy extra attention should be paid to the wishes and limitations of elderly cyclists in order to steer their mobility needs in safe directions.