How the time change affects traffic.

Road accidents

Various studies show an increase in the rate of road accidents immediately after the changeover to summer time. This is mainly attributed to the relative lack of sleep that many people experience due to the 'stolen' hour, but also to the fact that more journeys are made at dusk or in the dark. Even if not all studies come to this conclusion, it seems to make sense to prepare well for the changeover to Central European Summer Time (CEST) in spring (see tips on changing the time) or at least leave the car in the garage on the Monday after the changeover.
Conversely, there are indications that the changeover to standard time (winter time), when you get an hour 'for free', reduces the risk of traffic accidents. And summer time itself - apart from the time directly around the changeover - probably also has a positive effect, as peak traffic times tend to be during daylight hours.

Impact of the time change on timetables

Railroads in particular have always been affected by time changes - in the past even more so than today, because at that time local timekeeping still applied, meaning that time shifts occurred not just twice a year, but on almost every journey between two cities.
In order to keep the inevitable confusion within limits, the railroads introduced quasi separate time zones - Berlin, Munich, Stuttgart, Karlsruhe or Ludwigshafen time, which the railroads followed and which was displayed at the stations in addition to the local time. The standardization of times within Germany to Central European Time, which was demanded primarily by the railroad companies and introduced in 1893, simplified the situation considerably.

The time changes resulting from the summer time regulation, on the other hand, are actually a piece of cake and are now handled very routinely by Deutsche Bahn. The procedure is as follows:

When switching to summer time, trains miss the hour between 2 and 3 o'clock. Wherever possible, freight trains are simply sent on their journey earlier so that they arrive on time. S-Bahn trains that would only be running within the missing hour are simply canceled.
For night trains, any night-time stops are shortened in order to arrive at the destination without any delays.
All others for which this option is not available are simply late.
When switching to standard time (winter time), the hour is repeated between 2 and 3 a.m., so the night is longer.
Night trains then simply stop for an hour at a suitable station so as not to arrive too early.
S-Bahn trains that depart on the double hour depart 'twice' that night, which of course requires an increased deployment of vehicles and personnel.

Of course, traveling by train to a country that has no or a different summer time regulation is also problematic. Delays or even early arrivals are unavoidable here.

These problems are of course also conceivable with air travel, but all airlines plan their flights according to Greenwich Mean Time, so that the local time is basically irrelevant and only appears on the passengers' travel documents. Nevertheless, difficulties can arise in individual cases, such as in 2015, when the Turkish government postponed the time changeover at short notice, causing the departure times of all flights departing from Turkey to be delayed by one hour