Friday, February 21, 2003

Large railroad switchyards have a giant turntable in the middle of a star of tracks, so that a car or locomotive can be easily taken from one train on one track and attached to a different train on a different track. Just drive the locomotive onto the turntable, rotate however many degrees to reach the other track, and drive off. It is much faster than driving it down and around.

I notice that space seems to be at a premium in the downtown regions of large cities. One space-eater seems to be irreducible: the loading dock. You have to have a fairly large area for trucks to maneuver and back into position so that the forklifts can fetch off the cargo.

I can think of two ways to deal with this:

Move the loading dock

Park the truck parallel to the building and swing or slide out the loading dock to meet the rear of the truck. The depth of the loading dock needs to be greater than the turning radius of a fully-loaded forklift (with a little slop allowance!), and it has to support whatever loads the truck will disgorge. Using a cantilevered platform doesn't seem very robust, but you can contemplate supports on rollers under the outer edge of the dock.

When the truck is unloaded/loaded, the driver can simply drive away. If the loading dock becomes stuck, you're out of luck until it can be fixed. The loading dock is not well-sheltered from rain and snow.

Rotate the truck

The truck drives into a tunnel, and parks on the turntable. The turntable rotates the truck maybe 10 degrees, so that the rear of the truck is now at the edge of the loading dock. The loading dock has a wall on one side, but can be as deep as needed (just lengthen the tunnel). The turntable doesn't need to be a full 360 degrees, of course: you can make it what you like: the smaller the angular range the less floor space you need.

When the truck is unloaded/loaded, the truck can be rotated back into position if the tunnel is straight, or simply driven off (and let the empty turntable rotate back) if the tunnel jogs. An advantage to having a tunnel go all the way through is that ventilation is much easier.

The turntable is well-understood technology, doesn't involve major cantilevering, and can probably be unjammed by humans using pry bars.

There's a 3'rd option: a hybrid of the above, in which the driver parks parallel to the docking area, and the turntable rotates the truck into position. Ventilation is very easy and there is partial shelter from the elements. If the turntable section is a wedge, with the truck's nose at the center of rotation, the truck won't stick out into traffic.

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