HOW DO YOU GET PAST MISSION 4 ITS IMPOSSIBLE
Fortunately, your train's top speed is a fair bit higher than the target train. There's two good tactics for this.
One is to take advantage of setting the switch ahead of you shunting the target train onto the 2nd track before it's ready to do so, thereby sticking them behind a slower train early on and allowing you to pass with ease. This is a little difficult to pull off and requires repeatedly setting the route about the time the target train approaches the switch.
The other is to make good, careful use of the left-most tracks for passing trains and obstacles at certain points. Frequent reference to the map and care observing positions of oncoming trains is crucial to this.