In my city some bus routes has some alternative routes. For example, the line 1 for half of the fares it splits on line 1/ and make a longer route. Have I to map both line from the same start/end points on different routes or could I map only the difference for line 1/?

In my city some bus routes has some alternative routes. For example, the line 1 for half of the fares it splits on line 1/ and make a longer route. Have I to map both line from the same start/end points on different routes or could I map only the difference for line 1/?