Many work vehicles are so tall you would have to stand on one ladder to load or unload another from the rack on top. 

Enter a caption (optional)

This is hardly ideal, which is why most vehicle accessory companies offer racks that tilt down to the side of a box truck or van, so people can get at the ladders they carry.

With this more common configuration, the operator uses a handle to swing the rack to the side and then pulls it down to where he can reach the ladder and lift it off. 

Enter a caption (optional)

An Italian company, Gentili, came at the problem from a different direction. Their Harrier rack loads from the rear, sliding out like a drawer and then pivoting down on gas pistons. The ladder can then be removed from or strapped onto the rack. It doesn't matter if the vehicle is tall because the operator is provided with a pole that can be used to reach up, unlatch the rack, and then pull it down (or push it back up).