Sometimes when travelling between two stops, you arrive at Gothenburg C by train, for example, but then need to continue your journey by bus from the Nils Ericsson Terminal. A broken straight line is then displayed to indicate the change when you look at the journey on the map.
This line may also be shown at the beginning or end of your journey if you chose to travel to/from an address. In this case a walking route will be shown (in grey) from the address to the stop closest to the address. A straight broken line is then shown to the stop where you need to get on (and where you need to get off when you arrive).