DB_Delay
From 74 gigabytes of data, with 20 million entries of trains and many weather data, I created this chart, which contains many dependencies of weather and the train delay. But road accidents and fires in railway interlocking systems for example, also have an effect on the delay.
SOURCES
Train data - OpenDataCity (http://download.odcdn.de/zugsonar/)
Weather data - Deutscher Wetterdienst (ftp://ftp-cdc.dwd.de/pub/CDC/)
Weather data - Deutscher Wetterdienst (ftp://ftp-cdc.dwd.de/pub/CDC/)