During the mandatory winter equipment period in Austria (1 Nov – 15 April), what is the minimum statutory tread depth for winter tyres (M+S) on heavy buses (>3.5t)?

1. 2.0 mm
2. 5.0 mm for radial tyres (6.0 mm for diagonal tyres) on the drive axle(s)
3. 3.0 mm across all axles
4. 8.0 mm on front steering tyres only