What is the vehicle that is pulling cars?
The vehicle is a train.
    src        edge_attr  dst
0     0  to the right of    2
1     1   to the left of   28
2     2   to the left of    0
3     5  to the right of   18
4     5   to the left of   27
5     5   to the left of   24
6     6   to the left of   17
7     6  to the right of   24
8     6   to the left of   28
9     7  to the right of   19
10    7  to the right of   20
11    9   to the left of   26
12   11   to the left of   15
13   11   to the left of   17
14   11   to the left of   28
15   12   to the left of   18
16   14  to the right of   21
17   15  to the right of   11
18   15  to the right of   29
19   16   to the left of   25
20   17  to the right of    6
21   17          pulling   21
22   17  to the right of   29
23   17  to the right of   24
24   17  to the right of   11
25   18  to the right of   12
26   18   to the left of    5
27   19   to the left of   21
28   19  to the right of   23
29   19   to the left of    7
30   20   to the left of    7
31   20  to the right of   23
32   21  to the right of   23
33   21        pulled by   17
34   21  to the right of   19
35   21   to the left of   14
36   23   to the left of   19
37   23   to the left of   21
38   23   to the left of   20
39   24   to the left of    6
40   24   to the left of   17
41   24  to the right of    5
42   24   to the left of   28
43   24   to the left of   27
44   25  to the right of   16
45   26  to the right of    9
46   27  to the right of   24
47   27  to the right of    5
48   27   to the left of   28
49   28  to the right of   29
50   28  to the right of   27
51   28  to the right of   24
52   28  to the right of    6
53   28  to the right of   11
54   28  to the right of    1
55   29   to the left of   17
56   29   to the left of   28
57   29   to the left of   30
58   29   to the left of   15
59   30  to the right of   29