Tractor Trains

Warehouse tractors can be powered by gas, liquid propane internal combustion engines
or electric battery. They usually haul several trailers at a time and are fairly versatile
pieces of industrial equipment. Gas and LP gas powered vehicles are widely used where
materials must be hauled a relatively long distance or where these vehicles serve as the
connecting link among several buildings. LP gas and battery powered vehicles are
preferred where a considerable amount of tractor-trailer time must be spent inside the
confines of one building because of the noxious fumes emitted by straight gas tractors.
When tractor-trailer trains are used to support the shipping function, consider the following
factors:

•        If palletized material is to be held on the trailers until offloading into a carrier a
large amount of shipping floor space is wasted.
•        A better use of the tractor-train is to use it to transport materials into the shipping
department from other areas within the plant and to off-load the trailers immediately into
their set-out areas.
•        Since tractor-trains require a large amount of space to turn around, only straight-
line runs into the shipping department should be contemplated.
•        Right angle turns with a tractor-train consume less floor space than a U-turn, but
remember that tracking occurs so that the corner of a turn will be cut increasingly as the
number of trailers pulled increases.

Automatic Guided Vehicles (AGVs)

AGVs or driverless tractors have been used in warehouses and factories since the 1940s.
Initially they were rather slow in establishing themselves as a reliable and cost effective
means for transportation. At the beginning their guidance systems were marginal; some of
the earlier manufacturers even used war surplus guidance mechanisms in an attempt to
lower their high purchase prices. Fortunately, over the intervening decades reliability has
improved considerably. Some of the advantages and disadvantages are the following:

•        The conditions of the floors have to be fairly good and uniform in surface treatment.
Bumps, potholes, large cracks, railroad tracks and the like present special, although not
insurmountable problems. In other words, fix them!
•        AGVs can be readily sabotaged or damaged by disgruntled employees.
•        They are relatively high priced and require regular maintenance attention.
•        The savings in labor hours can sometimes justify their use.
•        They are especially effective when integrated into a larger, mechanized system.
•        Some AGVs are capable of being used as warehouse tractors, and can be taken off
their guidance lines for manual use.