Road accidents are marked by a seasonal effect, i.e. a rise or fall in mortality, whether small or significant, depending on several "temporal" parameters included in accidentology analyses. Thus, depending on the time of day, the day of the week, the week, the month, the year, or even the luminosity (day/night), road accidents and deaths differ.

Nowadays, accidentality is strongly correlated with traffic generated by good weather conditions, while poor conditions, while increasing the risk of accidents, generally dissuade users from driving or at least encourage them to be more careful.

For all road users, an increase in fatalities is noticeable during the summer period (June-July-August), as traffic is more intense during these three months. Nevertheless, the development of motorways, the banning of heavy goods vehicles and other complementary measures have made it possible to reduce road deaths during the summer. In 2020, the summer period was an opportunity for the French people to travel without distance restrictions, resulting in the usual peak in deaths in July, although deaths remained below those of previous years over this period.

Mortality among motorcyclists is also highest during the summer period, with an increase observed as early as April-May. The arrival of sunny days with better weather conditions leads to increased mobility of motorcyclists and moped riders, and therefore an increase in accidents involving them.

Similarly, the distribution of cyclists killed or injured in hospital by month of the year shows a seasonal aspect of accidentality. Conversely, pedestrian mortality is higher in the winter months, due to the extension of the night period and the reduced visibility of other road users.

In addition to months, the days of the week are also uneven in terms of mortality. It also varies from week to week, with a maximum generally reached in summer, more than double the minimum often reached in winter. Long weekends (Easter, Pentecost, Ascension, All Saints) have often proved to be the most deadly in the past. Today, travel is more spread out (especially in the case of the inclusion of public holidays in school holidays), and according to weather forecasts.