Comment by bombcar
1 year ago
What to do with late trains is a very interesting problem from a network stability perspective.
It’s somewhat akin to the packet dropping question, though packets don’t complain as loudly as passengers.
In a rail network with one train a day it’s not a big issue, but with regular service you can’t let a late train get out of control or it blows the entire network out of sync until you have some dead time - which is one reason some systems have an “hour of the dead” where no trains run - it lets it reset and get back to something sane.
Trying to build a system that has 15 minute heads and can handle a train going late or dying on the rails is really, really hard without ridiculously complexity like quad tracks everywhere and spare train sets at every station.
I agree that it's a hard and interesting problem. Yet other countries seem to be managing it better, or there is something structurally different.
I read somewhere that one of the key issues in Germany is that freight and passenger trains share the same network. While a delay of 15 minutes can be wildly problematic for a passenger train (missing connections, stranding at some godforsaken train station etc.), it is virtually irrelevant for freight. Then again, that should make it easy enough to always prioritize passengers over freight, but either that isn't being done or it's still insufficient.
The USA has the freight problem because trains can't pass each other unless there is a siding long enough for the train that is being passed; and the freight trains are too long.
Where there's double-track (or more) it's not as big an issue because the train can pass on the other side of the track (tracks are often handled as if they were a road with one lane going in one direction and the other going the other way, but you can swap around with signaling).
The other major solution (bandaid) is to add dwell time at stations so that there's room to make up - the timetable says when the train will leave not when it will arrive, and if it normally arrives five minutes early, it just waits; if it lost time and arrives one minute before departure, it will just be there a minute and the lost time is made up.
But while that may reduce the "worst case" scenario, it does make the average travel time longer.