Trailer restraints do much more than restrain trailers

Vehicle restraints were invented to help stop forklifts from tumbling from a loading dock and crippling or killing drivers. For nearly three decades, they’ve done that job well. But now they do more.

By Joe Manone

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Vehicle restraints were invented to help stop forklifts from tumbling from a loading dock and crippling or killing drivers. For nearly three decades, they’ve done that job well.

But they do more. They make loading docks more productive and support efficient supply chains. Modern restraints also reduce the risk of neck and back injuries to forklift drivers by reducing trailer drop – vertical trailer bed movement caused by the weight of forklifts traveling in and out of trailers - that can jolt forklift operators.

Restraints play a strategic role as part of ergonomic dock designs that protect employee health and wellness. In their original function, restraints secure trucks of any size, shape, height and configuration to the loading dock, while helping to prevent trailer-separation accidents (Figure 1).

Figure 1

Figure 1. A trailer that isn’t properly stabilized moves substantially in both the vertical and horizontal directions, causing problems such as damaged equipment and products, chronic back injuries to forklift operators, serious accidental injuries, and greatly decreased productivity.

Given these advantages, the selection of vehicle restraints is a business decision that deserves attention from multiple functions: warehousing and logistics managers, safety directors, operations management and executives. A restraining system that fits the work environment contributes to a safe workplace, a competitive supply chain and strong business performance.

Simple beginnings


Vehicle restraints are needed because wheel chocks alone proved ineffective for holding trailers at the dock during loading. Repeated jolts from forklifts can cause trailers to creep away from the dock until a gap opens at the dock edge (Figure 2).

Figure 2

Figure 2. With the advent of air-ride suspension trailers in the early 1990s, bed heights could fluctuate by several inches as left trucks added or removed loads. Such trailers could bounce and progressively “walk” away from the dock, a serious problem for forklift operators.

The forklift and driver then can fall to the pavement, with catastrophic results.

Aside from being unreliable and prone to slipping on snow or ice, wheel chocks provided no signal to let forklift operators know if they could safely load, or to tell truckers when they could safely depart. As a result, truckers sometimes pulled trailers away while a forklift was entering, again causing serious incidents.

The first vehicle restraints addressed the problem effectively. When a trailer is backed up to a dock, a hook inside a wall-mounted housing rotated up to grab the rear impact guard (RIG), holding the truck in place (Figure 3). If the trailer was secure, forklift drivers saw a flashing green light. When the RIG was released, they saw a flashing red light. Truckers, meanwhile, saw a red light when the trailer restraint was engaged.

Figure 3

Figure 3. Introduced in the late 1990s, the “fish hook” is designed to wrap around the rig to protect against every known form of trailer separation.

When it disengaged, they saw a green light, which told them they were cleared to leave(Figure 4).

Figure 4

Figure 4. Automated vehicle restraints like this reduce the potential for accidents at the loading dock. By supporting the rear of the trailer during loading and unloading, vertical and horizontal trailer movement is minimized.

This configuration, built on a national survey of thousands of trailers and five years of development, worked on 95% of trucks. In 1981, OSHA recognized the restraints as an acceptable alternative to wheel chocks. Companies of every size and across industries adopted the technology, which became fundamental to dock designs.

Changing landscape


Then, life at the loading dock began to change. Through the 1980s, companies pushed for more efficient supply chains and preferred trucks that could carry bigger payloads.

Trailers were switched to low-profile tires and rims to increase box size without increasing clearance height. Air suspensions cushion the ride, protect cargo and extend trailer life.

These new trailers – longer, wider and taller, with lower beds – challenged lift truck drivers. At the same time, plants demanded more productivity on the dock. Faster servicing of new trailers carrying wider, taller loads added to safety concerns.

Vehicle restraints had to adapt, holding on to RIGs at the typical 30 in. above the road, yet reaching down to secure low-bed trailers with RIGs as low as 12 in. above the ground. Modifications such as a low-profile nose extension on the restraint housing provided the necessary working range.

Adding complexity, some trucks had hydraulic rear liftgates for use at facilities that had no dock levelers. These units had no RIGs for traditional restraints to grab. The response was wheel-locking restraints. As the trailer backs in, an automatic barrier rod is positioned against and ahead of a rear tire. These restraints can secure virtually every trailer.

Gaining prominence

When supply chain efficiency became universally recognized as a key to competitive advantage, business saw a safe, productive loading dock as a key link in the distribution chain.

Yet new hazards emerged at the loading dock. Trailers with air-ride suspensions have a bed height that can fluctuate by several inches as lift trucks add or remove loads (Figure 5). These trailers have a natural tendency to bounce with the weight of loads and progressively move away from the dock. The bouncing can cause some restraint designs to lose their grip on the RIG.

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