I hit this the very hard way. A long loop of track, serving eight towns. All was well, until I electrified it, and started running electric trains. The first line was OK, so I switched the trains on the other track/line (running in the opposite direction) to electric as well. Nightmare. Everything backed up and jammed, taking me from +8M profits to -8M losses in a couple of minutes.
The cause? One tiny sliver of non-elecrified upgraded track, formed when the game automatically chopped the track into a sliver at a level crossing.
The visual clues are useful, once you realise how they work. The high-speed track upgrade, for example, highlights from station to station indicating a contiguous section of track. I didn’t realise the electrification upgrade does the same thing.
The other clue would have been the lines themselves. A working line shows colour. If the trains cannot run, the line disappears. The booby trap was that I didn’t spot one of the two lines was showing arrows in both directions after my “upgrade”. Because, the trains had to reverse around the entire loop to get to the next station beyond the break in the line.
So, there are visual clues to show when things are not happy. But I have to agree, electrification should be a one-click thing to electrify all track between stations.
And I do like the “view” colouring idea to show electrified versus non-electrified track. The same might be said about high speed and regular speed track.