Where is the gravel?
The gravel is on the highway.
    src        edge_attr  dst
0     0   to the left of    2
1     0   to the left of   16
2     1   to the left of    7
3     2  to the right of    0
4     2               on    1
5     2   to the left of   10
6     2   to the left of   16
7     2   to the left of    9
8     3               on    1
9     3   to the left of    7
10    4  to the right of   13
11    4   to the left of    6
12    5   to the left of    8
13    6  to the right of   16
14    6  to the right of    4
15    7  to the right of    3
16    7  to the right of    1
17    7  to the right of   15
18    7               on    1
19    8  to the right of    5
20    9  to the right of   10
21    9  to the right of    2
22   10  to the right of    2
23   10   to the left of    9
24   13  to the right of   14
25   13   to the left of    4
26   14   to the left of   16
27   14   to the left of   13
28   15   to the left of    7
29   16  to the right of    2
30   16  to the right of   14
31   16   to the left of    6
32   16  to the right of    0