What vehicle is this, a truck or a bus?
That is a bus.
    src        edge_attr  dst
0     1  to the right of    7
1     1  to the right of    2
2     1   to the left of    4
3     2  to the right of    7
4     2   to the left of    1
5     2   to the left of    4
6     4  to the right of    7
7     4  to the right of    2
8     4  to the right of    1
9     5   to the left of    9
10    5  to the right of    6
11    6   to the left of    5
12    6   to the left of    9
13    6  to the right of   11
14    7   to the left of    2
15    7   to the left of    1
16    7   to the left of    4
17    8  to the right of   10
18    9  to the right of    6
19    9  to the right of    5
20   10   to the left of    8
21   11   to the left of    6