Ticket to Ride "Longest Path of Routes"
Spurs are not included.[1] Being connected is not sufficient; the routes must form a continuous path.

The rules say

The player who has the Longest Continuous Path of routes receives this special bonus card and adds 10 points to his score. When evaluating and comparing path lengths, only take into account continuous lines of plastic trains of the same color. A continuous path may include loops, and pass through the same city several times, but a given plastic train may never be used twice in the same continuous path. In the case of a tie for the longest path, all tied players score the 10 point bonus

Let's use the following network as an example:
   A-----B
          \
           \
            C-----D------E
            |
            |
            F

How many routes are in this longest continuous path? Obviously, it's at least 4 (A-B, B-C, C-D, D-E). Is there a way of including C-F without jumping (not continuous) or revisiting a route (explicitly disallowed)?

If you travel along the path A-B-C-D-E, you'd need to jump or backtrack to visit C-F.
If you travel along the path A-B-C-F, you'd need to jump or backtrack to visit C-D.
If you travel along the path F-C-D-E, you'd need to jump or backtrack to visit B-C.

So no. The longest continuous path consists of four routes.
This is confirmed through play with multiple groups and through use of the official electronic version. Note that at least one map (Asia) awards points for largest network, which includes forks (though this counts cities rather than routes).


Unless you can loop back. For example, the following has a continuous path of 5 routes:
A--------B--------C
        / \
       /   \
      D-----E