| Value | Category | Cases | |
|---|---|---|---|
| bitumen | 24 |
12.1%
|
|
| concrete | 9 |
4.5%
|
|
| dirt | 63 |
31.8%
|
|
| gravel | 74 |
37.4%
|
|
| n/a | 27 |
13.6%
|
|
| other | 1 |
0.5%
|