Which kind of vehicle is the train pulling?
The train is pulling cars.
    src        edge_attr  dst
0     0               on   11
1     0   to the left of    4
2     1  to the right of    5
3     1               in    9
4     1  to the right of   12
5     1  to the right of    8
6     2   to the left of    4
7     2   to the left of   18
8     2        pulled by   11
9     4  to the right of    2
10    4   to the left of   17
11    4  to the right of    0
12    5               on   14
13    5  to the right of   12
14    5   to the left of    1
15    6  to the right of   16
16    6   to the left of   15
17    8   to the left of    1
18   11          pulling    2
19   12   to the left of    5
20   12   to the left of    1
21   15  to the right of    6
22   15  to the right of   16
23   16   to the left of    6
24   16   to the left of   15
25   17  to the right of    4
26   17  to the right of   18
27   18  to the right of    2
28   18   to the left of   17