Stop when the car comes into the station. At this time, the car has a lot of kinetic energy. If it brakes, it will be converted into internal energy and lost. If you let it go uphill when entering the station, it will be converted into gravitational potential energy and stored, reducing the mechanical energy consumed by braking.

When the car leaves the station, it is in a static state, has no kinetic energy, and needs to consume the chemical energy of fuel to start and move. If you go downhill, you can convert gravitational potential energy into kinetic energy, which is convenient for starting, fuel-saving and energy-saving.

So the answer is: part of the kinetic energy when the car enters the station is converted into gravitational potential energy, which reduces the mechanical energy consumed by braking; When the car leaves the station, the stored gravitational potential energy is converted into kinetic energy, which plays an energy-saving role.