Something like this:
void SetTurnouts(int RouteNumber,int t0,int t1,int t2,int t3)
{
posnTrackSwitch[0] = t0;
posnTrackSwitch[1] = t1;
posnTrackSwitch[2] = t2;
posnTrackSwitch[3] = t3;
Serial.print("Route ");
Serial.print(RouteNumber);
Serial.println(" Active");
}
It'll make your code a lot shorter, but it's less than ideal - if you ever add switches, it'll have to change as will all calls to it. I'd be inclined to make the system more data driven and have an array of structs containing the route numbers and corresponding turnout settings. Then the code would be simpler still and more resistant to change.
That can come later though - the last thing you need now (to echo Robin2) is more code without doing some testing & debugging of what you have.