Hello!
I´m happy to explain the mechanics of traveling in more detail:
Every person in the game has a fixed place to live, which does not change. If a new house is build, people move in and they stay there for the rest of the game unless it is destroyed.
On a regular basis every person is looking for a place to work, to shop and a place to spend their free time.
They look in a 20 minute radius of travel time for such a place (this is known among the community as the “20 minute rule”). To calculate the travel time to the destination every possible route is taken into account. This might be as simple as just walking or driving somewhere, or more complex like walking from their home to a bus stop, going to the train station, using the train to travel into another city, there getting on a tram and then walking from the tram stop to the destination. Here also frequency comes into play. The more vehicles there are on a line, the shorter the expected waiting and therefore travel time will be.
When all possible places are calculated, people decide based on a formula, which one they choose. Generally, the closer the place is in regards of travel time, the more it is preferred. In addition to that people tend to stick to their current workplace (also shopping / leisure) for a longer period.
So over time, the place might not change, but the preferred way of getting there. For example when people get cars, they might switch from using the train to using the car, if it is faster to go to the next city or visa versa when for example faster or more trains are used. On the other hand new travel options also open more work place (shopping / leisure) options for people to choose from.
In conclusion, there is no limit on how often people can switch lines when the travel or how far (distance) they go, it mostly depends on time.
Best Regards
Tom (Community Manager)