| Value | Category | Cases | |
|---|---|---|---|
| 1 | Surface tunnels | 1753 |
4.2%
|
| 2 | French tunnels | 287 |
0.7%
|
| 3 | plastic houses | 10047 |
24.3%
|
| 9 | not stated | 39 |
0.1%
|
| Sysmiss | 29302 |