Is there a bus or a fence that is gray?
Yes, the bus is gray.
     src        edge_attr  dst
0      0           behind    3
1      0      in front of    1
2      0  to the right of   17
3      0  to the right of   13
4      0  to the right of    8
..   ...              ...  ...
103   18   to the left of    9
104   18  to the right of   14
105   18   to the left of   13
106   18   to the left of    1
107   19             near    2

[108 rows x 3 columns]