| Year | Month | Days | Number of stations |
| 1988 | 1 | 21 | 88 |
| 1992 | 1 | 29 | 74 |
| 1994 | 1 | 16 | 97 |
| 1999 | 2 | 17 | 78 |
| 2000 | 1 | 11 | 75 |