What's pulled by the train?
The train car is pulled by the train.
    src        edge_attr  dst
0     1  to the right of   18
1     1   to the left of    6
2     1  to the right of   20
3     1  to the right of    8
4     2  to the right of   17
..  ...              ...  ...
60   18   to the left of    6
61   18   to the left of    1
62   20   to the left of    6
63   20  to the right of    8
64   20   to the left of    1

[65 rows x 3 columns]