Mechanical dock shelter is the most commonly used because they cater for a mixed vehicle fleet with curtains that extend in from the sides and head allowing a vehicle to push through and keep the worst of the elements at bay. The curtains are designed to flex but maintain contact with the rear of the vehicle to maintain the "seal".
When the vehicle reverses on to the sponge dock shelter it compresses the foam as far as the dock buffers allow thus creating a seal between the vehicle and the building. The retractable frame is made from galvanized steel to make sure it lasts the course when exposed to the elements and just in case the shelter gets accidentally hit the arms are designed to retract out of harm's way by moving back and up.
Mechanical dock shelter are commonly used on ambient unheated or part heated warehouses where weathering of the opening and protection of the goods are the main criteria
Other dock shelter picture show: 
Complaint
