What counts as a double route: any two routes between the same cities, or only parallel routes of the same length?

Question

Accepted Answer

Any two routes linking the same two cities count as a double route, even when they are drawn apart or differ in length (for example Stavanger-Kristiansand). The English rules never require them to be parallel or equal, and an answer relayed from the designer agrees. Some players, and some translated rules, insist on parallel routes of equal length, so check with your group.

Ticket to Ride: Nordic Countries

What counts as a double route: any two routes between the same cities, or only parallel routes of the same length?