So trailer specialists in the Technology & Maintenance Council of the American Trucking Associations have written a set of guidelines, "Ergonomic Design Parameters for Safe Maneuvering of Converter Dollies," also known as Proposed Recommended Practice 756(T), that fleet managers can use when buying new dollies. The RP is now out for voting approval by TMC members.
The tips in the RP could also be consulted when repairing or modifying existing units that might not have everything to ease the chore of moving them into place when coupling or uncoupling double- or triple-trailer rigs. Hard-to-handle equipment like this can strain muscles in the back, arms and legs, but these can be minimized with properly-thought-out designs.
First, the handles that should be attached to the sides of a drawbar: "Manufacturers are encouraged to provide lifting handles or locations for two points of contact, excluding the drawbar eye," the RP says. "Ideally, the handle design should provide adequate size for gloved hands and be positioned or hinged to avoid damage."
Next, balance: A dolly should be built so it's slightly front heavy when standing alone, so that "the force required to lift a dolly should not exceed 85 pounds at breakaway," the RP continues. "This measurement is taken from the center of the eye with the brakes released. The dolly tip-up/balance point should only occur when the drawbar eye is 37 inches or higher from the ground." A spare tire-wheel assembly can serve as a rear-mounted counterweight, or one of correct mass can be bolted or welded to the frame.
"The 85-pound requirement was based upon acceptable ergonomic conditions for most fleets," says Gary Gaussoin, vice chairman of Silver Eagle Manufacturing and head of the TMC committee that wrote the RP. "The 37-inch dimension is based upon the industry standard hitch height of 34 inches and wanting to keep a positive downward force in the hitch. Trying to push a dolly into the hitch and close the latch is an opportunity for injury" if the tongue suddenly swings up.
Jacks and casters under the drawbar should be easy to use, the RP states, and the lifting mechanism should not auto-rotate downward so the jack strikes the pavement while traveling down a highway. Also, there should be a storage area for air hoses and electrical lines, drain valves and electrical plugs should be located where they're easy to reach, and metal parts should be free of sharp edges and corners.
Proposed RP 756(T) complements RP 721, "Practices for Safe Maneuvering of Converter Dollies." More information about TMC's many recommended practices and the Technology & Maintenance Council itself is available at http://tmc.truckline.com.