What is the train on?
The train is on the bridge.
    src        edge_attr  dst
0     0   to the left of   11
1     0               in   10
2     0   to the left of    1
3     1  to the right of    3
4     1  to the right of    9
5     1               on    4
6     1  to the right of    0
7     2   on the back of    1
8     3               in   10
9     3   to the left of    1
10    7   to the left of   12
11    7               on    4
12    8               on    4
13    9   to the left of    1
14   10            above    1
15   11  to the right of    0
16   12  to the right of    7