Max flat speed: 12.15km/h
You can not lower peat tiles by digging, be careful when dropping dirt, as raising a peat tile cannot be easily undone. If the northwest corner is adjacent to terraformable tile types that corner can be lowered through digging.
Peat tiles can be lowered using the Level command if all corners are higher or level to an adjacent flat tile. A digging skill of 70 is required to do this.