| Value | Category | Cases | |
|---|---|---|---|
| bitumen | 20 |
21.3%
|
|
| concrete | 7 |
7.4%
|
|
| dirt | 29 |
30.9%
|
|
| gravel | 30 |
31.9%
|
|
| n/a | 8 |
8.5%
|