What is the train on?
The train is on the railroad tracks.
    src        edge_attr  dst
0     1   to the left of   13
1     1  to the right of    3
2     1   to the left of    2
3     2  to the right of    1
4     2   to the left of   13
5     3   to the left of    1
6     4  to the right of    6
7     5   to the left of    8
8     5  to the right of   10
9     5  to the right of   12
10    5      standing by    8
11    5      standing on    6
12    6   to the left of    4
13    6   to the left of    7
14    7     covered with    3
15    7  to the right of    6
16    8  to the right of   15
17    8  to the right of   14
18    8  to the right of   12
19    8  to the right of    5
20    8  to the right of   10
21    8               on    7
22   10   to the left of   14
23   10   to the left of    8
24   10  to the right of   12
25   10   to the left of    5
26   10    standing near    8
27   12   to the left of   17
28   12   to the left of   15
29   12   to the left of    5
30   12   to the left of   10
31   12   to the left of    8
32   12   to the left of   14
33   13  to the right of    2
34   13  to the right of    1
35   14  to the right of   12
36   14   to the left of    8
37   14  to the right of   10
38   15  to the right of   12
39   15   to the left of    8
40   15   to the left of   17
41   16      filled with   13
42   17  to the right of   12
43   17  to the right of   15