Complex sentence: Time to travel from one city to another by bus is most often longer than for the same journey on the train because bus lines are less straight, as they pass through many small towns that are not served by railway.
Split into simpler sentences: Time to travel from one city to another by bus is most often longer than for the same journey on the train. This is because bus lines are less straight, as they pass through many small towns that are not served by railway.