Trace a Route Hint

Regard each design as a street map. If one were able to trace a map with a pencil, traversing each line (street) precisely once, what can be said about the number of streets that meet at each intersection point? [Note that although one may visit a particular point of intersection multiple times, any street used to enter that intersection must be paired with a street used to exit it – unless one were to start or end a journey at that point!