What is the purpose of the 'Anti-Slip Floor Covering' (Rutschhemmender Bodenbelag) legally mandated in public passenger buses?

1. To reduce tire slip by increasing traction between the road and the driven axle
2. To make wet steps safe without cleaning because the surface rating alone prevents every fall
3. To replace handrails for standing passengers when the bus accelerates or brakes
4. To prevent standing and moving passengers from slipping and falling on wet, snowy, or polished floor surfaces during vehicle maneuvering and boarding