What's the train on?
The train is on the platform.
    src        edge_attr  dst
0     1               on    0
1     1  to the right of    7
2     2  to the right of    7
3     2   to the left of    4
4     4  to the right of    2
5     4   to the left of    6
6     4   to the left of    5
7     5  to the right of    6
8     5  to the right of    4
9     6   to the left of    5
10    6  to the right of    4
11    7   to the left of    2
12    7   to the left of    1