To park a car with a trailer on a **slope**, it is important to take additional measures to ensure that the vehicle does not move. One way to do this is by using **wheel chocks**, which are wedges placed between the vehicle and the road. This is especially relevant on slopes, as gravity can cause the vehicle to move if it is not properly secured.

- **Wheel chocks**: Appropriate wheel chocks should be used, and not improvised with stones or other objects. Wheel chocks help keep the vehicle in place when parking on a slope.

- **Alternative to wheel chocks**: Another option is to turn one of the front wheels towards the curb. On an uphill slope, the wheel should be turned towards the center of the road, and on a downhill slope, towards the outside.

These measures are necessary for vehicle combinations, such as a car with a trailer, when parked on slopes, thus ensuring that the vehicle does not accidentally move.