In which case is it permitted to cross, make a U-turn or reverse a vehicle on an expressway or automobile road?

1. ①A car driver makes a U-turn into the opposite direction through a gap in the median because traffic is heavily congested
2. ②A truck driver slowly reverses along the shoulder after slightly passing the entrance to a rest area
3. ③A bus driver cuts across the lanes into the opposite carriageway to avoid an accident scene ahead
4. ④A road maintenance vehicle reverses because it is strictly necessary for emergency work at a traffic accident