What is the gray vehicle?
The vehicle is a train.
    src        edge_attr  dst
0     1   to the left of    8
1     2   to the left of    8
2     3   to the left of    6
3     4  to the right of    7
4     6  to the right of    3
5     6               on    9
6     7   to the left of    8
7     7   to the left of    4
8     8  to the right of    2
9     8  to the right of    1
10    8  to the right of    7