Rules state that:
A train may not end its move on a track segment or junction tile that contains another train. (2)
but notes also an exception:
A train may end its move on one track segment of a bridge or double curve tile even if another train occupies the other track segment. (2)
which seems quite natural and reasonable. Also:
There is no limit to the number of trains allowed on a town tile at the same time. (2)
which again seems natural especially that we start the game with all the trains on the town tile.
But there is another case which is interesting. Dead ends (1). It seems natural that two trains can be on the same tile at the same time if one of them is on a dead end while the other is on other track segment. Such would be the case with tile  on Figure 10 (2) and tile  on Figure 11 (2). Also the top right tile on Figure 11 (2) could hold 3 trains at the same time with such rules.
Is this not allowed by the rules on purpose or is this just a mistake or forgotten case?
Also some other threads (Junction Tiles In Regards to Derailment Die Rolls, Questions about ambiguities with speed limits, Please clarify ending your turn on a junction. And counting steam.) suggest (if I understood them correctly) that the rules require a player stopping on a junction to point on which track segment the train is (as this could force or prevent derailment roll). In such case it is obvious which track segments are empty and which are occupied.
So we could go even further and allow any number of trains coexist on a single tile providing that it is either a town tile or all trains are on different track segments/dead ends. It would also work well with +1 steam point for passing a train without requiring a player to pay for a train which is on other junction track segment.
Why is it not so?
By the way definition of dead end seems logically incorrect. It goes following:
A track segment that does not connect two tile edges. (2)
All would be clear if not the definition of the track segment which goes following:
A single section of track that connects two tile edges. (...) (2)
So a dead end by definition cannot be track segment as it does not connect two tile edges (also by definition).
All in all it seems obvious what is what but I think that if we do terms definitions (which is a good thing!) we should make them consistent.
In all cases my quotes are for second edition (Valley Games Inc.) rules. But as far as I know the rules for first edition are same (or are intended to be same).