An active trip is the trip currently used by SityTrip when you add places from a destination, a place sheet, or the map.
This allows for quickly adding places to the right trip, without having to select it each time.
Open the travel selection window.

Select the trip you want to set as active.

The selected trip becomes the active trip.

If a trip is active, the button turns red. A message also indicates the name of the active trip, for example Active trip: Trip to Paris.

➡️ See also: How to add places to your trip?