A few years ago, the MVG, Munich's public transportation system, altered the nighttime schedule for S-Bahns from running every 10 minutes to only every 20. The lower volume of passengers on the trains during the night, which required a less frequent operation schedule, was the reason for this change in train frequency.
However, fears have surfaced recently that the longer wait between S-Bahns may actually be more dangerous both on and off of the streets.
One of the concerns is that if the S-Bahns run so infrequently and the people do not want to wait, they might decide to take their cars instead. This could potentially result in more people driving under the influence of alcohol in order to get home after a long night out. Fatigue is a particular danger while in the driver's seat, as it reduces awareness and concentration.
On the S-Bahns and at the station, a long wait be the source of many problems, as well. Not only might it anger the waiting passengers, but it could conceivably lead to violence on the platforms. Though it is better to take the S-Bahn in groups, waiting alone at a station for an extended length of time makes passengers a target for lurking strangers.
Safety does not come cheap. The changes made to the system and the S-Bahn frequency would cost around 300,000 euros, but in the long-term this could be a wise investment.