I don't, this is just my personal experience with passenger rail in southwestern Germany. The smaller lines with 1-2 trains per hour are usually extremely reliable, while the lines on crowded tracks are usually delayed, or cancelled completely. Note that many of the reliable lines I regularly used over the past 10-15 years ran on track equipment from the 19th century, some still with wing signals and switches operated via pulleys. (Anecdotally, I never experienced any technical problems with this old equipment as a passenger, the technical problems usually started after modernization).
> Even this I'm not quite willing to accept without citation; the railway timetables in the 70ies and 80ies, especially after the oil shock, were quite dense.
The factor of 2-3 was for my local network (which was converted to an S-Bahn network a few years ago, and a 30 minute frequency was introduced, with 15 minute frequency during peak hours). Some parts of that network only had 1-2 trains per day from the 70ies to the mid-90ies.
Btw. Wooden sleepers laid in the 19th century have completely rotted away by now; it's impossible for the line track itself to be that old (except very slow speed shunting tracks, maybe.)
Do you have a citation for this?
The people I know from the DB bubble are telling me that while some places have not enough track (e.g. the infamous Frankfurt-Mannheim/Riedbahn), but the everywhere problem is that there's just fault over fault over fault in tracks (often switches, but even tracks themselves) and trackside equipment.
> […] the number of trains per hour was increased by a factor of 2-3 […]
Even this I'm not quite willing to accept without citation; the railway timetables in the 70ies and 80ies, especially after the oil shock, were quite dense.