Another easy way, if you have the cash, is to loop one section of the tracked route off and put a station in, doesn't matter for what, just so when you create the route for the new train, it has that special stop as part of its route, as well as your actual starting and ending points. Then the train will always appear on the correct track. Once the train is completed and starts off on its route, then pause, ADD your actual intended track route, then delete the extra stop on its schedule, delete the extra stop station and approach side trip tracks, leaving only the direct route you originally intended. Using this method you don't have to wait for another train to pull into the origination station.

@jetals1, are you able to start trains on those shorter routes? The trains must have a valid connection on on all the stations between the origin and destination stations..
Also see 7 Feb, 2021 @ 8:24pm "One of less obvious cases where this might not work is when you layed track exiting a station but the signal post at the station exit has not been created...."

@pommefatale Trains will NOT always go to the shortest route. I have on several occasions laid a section of track to shortcut a loop. Many trains would still take the loop rather than the shortcut.

If you add a switches to a piece of track, remember that the trains will always prefer the shortest route. So if you add a switch which creates a longer route to the same destination, this piece of track will only be used if there is oncoming traffic on the shorter route.

Please accept Solution Three (You have cash to burn)
1. Pause the game
2. Place the (cheapest) engine on the station's track by entering the new route
3. Repeat step 2 until you have an engine on the track you needed an engine.
4. Get your refunds for the excess engines by deleting them.
5. Complete the route orders for the train, and upgrade the train to your desired spec.
6. Unpause the game.

I noticed trains are always positioned on a track with the shortest *possible* route. Adding train tracks on the inside of an already curved track is therefore usually not a problem.
One of less obvious cases where this might not work is when you layed track exiting a station but the signal post at the station exit has not been created. Even if you have created a shorter route, the trains will not enter the station on this track because the signal post is absent. This happens more easily when (parts of) your connected track is/are elevated (e.g. on a bridge). You can add the signal post by adding a short stretch of track leaving left or right of your track. When you remove this added switch, the signal post will remain.

removing double track or even 4 lines with connectors is a pain when laying second and up lines create z short section then run long line to short of destination . if need to remove main line to get to junky crossover when line is deleted will only lose the short section.

Good advice. My problem is when I have double-tracked and then placed a crossover switch, I can never click that section only to remove it, even when I zoom and twist, etc. It's an interface thing, methinks. Keep on Rollin'!

Kwel. I can't wait to try this once I get Steam reinstalled and running.

If you play the Northeast scenario where you have to transport immigrants from New York to Washington DC, you definitely want a line that runs exclusively for that train. I usually run two trains on the same line, adding a third track between Wilmington and Philadelphia as that is where the two converging trains on the same track will meet, one will go on the side track and one stay on the mainline, this helps save time when transporting those immigrants. In this scenario, try to keep either North or South of the mainline track your laying free of encumbrance until you have a single dedicated line for your express between New York and D.C. If you should extend to the north or south, you will find you must lay switches to get around those tracks, sooner or later aother train you have added will get onto the track due to the switching, and your efficiency at delivering those immigrants will be greatly reduced.