Hello,
You can apparently use
F1/F2/F3 keys on your keyboard, when you are near a track switch.
I tested this on Train Valley and it works. It's hard to see when you're in a train, but it works.
This only works when you are very close to the switch, about a train's length.
So, when you're riding and approaching a switch, just hold one of the F keys to go left/center/right and it'll switch as soon as you're close enough.