Shock buffers consist of a plate and a spring. They are located at the front and rear of locomotive, coach or wagon. The buffers cushion the shocks that occur during docking and running due to traction and braking jolts. They are closely associated with the traction units. In Europe, freight wagons are still equipped with screw and turnbuckle couplings which have to be operated manually. Only passenger trains (high-speed trains, railcars, trams, etc.) are equipped with automatic couplings with central buffer.