What's the train on?
The train is on the bridge.
    src        edge_attr  dst
0     0               in    1
1     0               in    7
2     0               in   21
3     0  to the right of    1
4     1   to the left of    0
5     2   to the left of    6
6     3  to the right of   12
7     4   to the left of   19
8     4   to the left of   12
9     5   to the left of   19
10    5   to the left of   12
11    5               on    4
12    6  to the right of    2
13    8               in    7
14    8               in    1
15    8  to the right of   16
16    8  to the right of   18
17   10  to the right of   17
18   12   to the left of    3
19   12  to the right of    4
20   12  to the right of    5
21   13               on   12
22   13  to the right of   18
23   14  to the right of   17
24   16   to the left of    8
25   17   to the left of   10
26   17   to the left of   14
27   18  to the right of   20
28   18   to the left of   13
29   18   to the left of    8
30   19  to the right of    5
31   19  to the right of    4
32   20   to the left of   18