What vehicle are the people on?
The people are on the train.
    src        edge_attr  dst
0     1   to the left of    5
1     2             near    6
2     2   to the left of    6
3     3          next to    6
4     3               on    6
5     3             near    6
6     3  to the right of    6
7     4               on    1
8     4   to the left of    5
9     5  to the right of    4
10    5  to the right of    1
11    6   to the left of    3
12    6  to the right of    2
13    6             near    3
14    6             near    2