Vehicle restraint systems help create safer dock areas

Key concepts Restraints must address four types of trailer separation from the dock: trailer creep, unexpected departure, landing gear collapse, and trailer unending.
By Kyle Nelson, Rite-Hite Corp., Milwaukee, WI February 1, 2001


Restraints must address four types of trailer separation from the dock: trailer creep, unexpected departure, landing gear collapse, and trailer unending.

Selection criteria include constant engagement, clear communications, durability, and ease of maintenance.

Training of dock employees and visiting truck drivers is essential.

Vehicle restraint systems are a major factor in making the loading dock a safer workplace. However, it is dangerous to assume that the mere presence of the equipment erases the specter of a forklift and driver falling over the edge of the dock because a truck trailer shifts or pulls away unexpectedly. Actual safety gains result from carefully choosing the restraint system that best suits the operation, maximizing the investment by maintaining it, and training dock area employees to use the equipment properly.

A restraint that does not meet basic safety and operational criteria and provide full-time security is no longer a safety device, but an increased hazard, because a false sense of security exists. The same holds true for standard wheel chocks, which frequently go unused, and can also be ineffective against most types of trailer movement.

The consequence of even one restraint failure is often disastrous, including crippling or fatal injuries. Therefore, the device chosen must be reliable and effective under all operating conditions.

Operational considerations

There are two basic styles of mechanical trailer restraints:

  • Restraints that attach onto the rear impact guard, or ICC bar

    • Locks that secure the trailer’s rear tires.

      • ICC-style restraints are more common; however, for lift gate trailers and other vehicles that lack an ICC bar, wheel-locking restraints offer an effective alternative.

        Almost all ICC-bar restraints have two basic components: a device that holds the trailer to the dock, and a communications system of lights and signs that tell the forklift operators and truckers when the trailer is secured and when it is not. Dock employees typically activate and release the restraint system from a push-button panel located adjacent to the dock door.

        Variations of the two common types are numerous. Restraints are available with a variety of barrier configurations and can be powered mechanically, pneumatically, or hydraulically.

        Rotating hook style restraints have been around the longest, and represent the majority of units installed. Popularity of this restraint design is a result of the level of safety provided, compared to vertical barrier systems, which are common on lower cost models.

        Among the various operational modes, those that are automatically positioned by the trailer (vs those that must be manually powered into place) represent the greatest number of installed units. Consult with a knowledgeable equipment representative to help select the restraint features that will ensure the safest operation at the lowest ownership cost.

        How safe is safe enough?

        The biggest consideration when choosing a restraint is usually the degree of protection required against trailer separation. There are essentially four types of trailer separation from the dock that can lead to forklift accidents, and different restraint types have varying degrees of effectiveness against each problem. (Note: Wheel chocks, although OSHA approved, are the least effective means of restraining a trailer.)

        Trailer creep , which is the gradual inching of the trailer away from the dock due to the impact of the forklift traveling in and out during loading and unloading, is prevented by all restraint types. Trailer creep causes the dock leveler lip to eventually lose contact with the back of the trailer and create a dangerous gap between the trailer and dock.

        A more pronounced form of creep, known as dock walk, has become common in recent years due to the increased number of trailers with air-ride suspensions.

        Unexpected departure occurs when the driver mistakenly pulls away before loading or unloading is complete. This situation can usually be controlled by both vertical barrier and rotating hook restraints. Units with hooks can offer better protection than vertical barriers, however.

        Landing gear collapse occurs when a trailer is detached from the tractor during loading/unloading (“spotted”). This potential hazard can result in serious injury, and only some restraints effectively address the danger.

        Vertical barriers, by design, are at a disadvantage in addressing the separation that can result from landing gear failure. Rotating hook restraints, on the other hand, create a trap that can control both the horizontal and vertical movement of the ICC bar when landing gear fails.

        Trailer upending can result from a heavy load being placed in the nose of a spotted trailer, which causes the trailer to tip. Again, only rotating hook restraints effectively address this problem.

        Other selection factors

        In addition to how well a restraint addresses all four types of trailer separation, several other criteria should also be considered when making the equipment selection.

        Constant engagement. The restraint should maintain consistent, solid contact with the ICC bar during all phases of loading and unloading as the trailer bed height changes with the addition or removal of cargo. When a fully loaded trailer is hooked and pallet loads are removed, the trailer bed floats upward. The ICC bar could become disengaged from the restraint if the restraint does not float upward at the same rate to compensate for the change in height.

        Air-ride suspensions, which can cause the bed height to depress up to 8 in. when the forklift travels onto the trailer, causes some restraints to lose contact momentarily with the ICC bar, seriously threatening safety. Look for a restraint that holds sufficient upward pressure against the ICC bar under all conditions.

        Clear communications. Restraint warning lights, signals, and signs easily understood by all employees and visiting truck drivers should be used. The ideal communication system includes universally understood flashing red and green lights-both outside and inside-telling truck and forklift drivers when they can safely move. Some manufacturers offer foreign language signs to aid this communication.

        An automatic, audible alarm that alerts forklift drivers when a trailer is not properly engaged is also critical.

        Damage protection. The restraint should be durable enough to withstand the impact of backing trailers as they come into position against the dock. Restraints that cannot withstand this impact are subject to severe damage.

        Similarly, the restraint’s communication system should not rely on sensitive sensor wands, treadle plates, or any component that is exposed to potential damage.

        Protected components. Restraints are routinely exposed to rain, snow, dirt, and debris. Therefore, equipment should have a protective coating, such as zinc or cadmium plating, on inside and outside surfaces. Components should be constructed from materials that resist rust and corrosion. Drive components should be sealed against dirt, which can cause rapid wear.

        Restraints that mount on or in the ground, rather than on the dock face, are more vulnerable to damage from dirt and moisture. Also, ground levels change as freezing and thawing occur, which could affect the operating range of the equipment. Restraints that mount above the ground have an extra measure of protection from water and dirt, and facilitate snow plowing and debris sweeping in front of the dock.

        Ease of maintenance. Restraints should be designed so they require only minimal maintenance and continue to operate even when only sporadic attention is given. All safety equipment requires some routine maintenance to ensure optimal performance at all times. Do not accept any claims of “no maintenance required,” and check the product owner’s manual for clues to true maintenance requirements.

        Integrating the system

        Vehicle restraints present opportunities to customize the total dock safety system to suit specific needs. For example, systems often include interconnects or interlocks that activate the restraint automatically when the dock leveler is used, or ensure that the leveler or dock door cannot be operated until the system engages the trailer.

        However, for maximum safety the restraints should never automatically release the truck when the dock leveler returns to the stored position, as many conditions require that the leveler be stored in order to place the last pallet on the trailer. Forfeiting engagement prior to completing the loading could create a serious accident. Release of trucks should be a separate, conscious act under the direct control of dock attendants.

        Proven reliability

        There are two critical questions to ask when considering any vehicle restraint. “To what degree will the product help minimize my accident risk?” “Has the product stood the test of time so that I can be sure of the value of my investment?” Simply put, if a restraint does not work, employees are at risk and overall ownership costs increase.

        Because of the number of varied and often compelling design differences between restraints, the main issue can become clouded when evaluating the many available options. Request to see the manufacturer’s complete list of repeat users who have purchased the restraint being considered to be assured that your investment is a sound one.

        -Edited by Ron Holzhauer, Managing Editor, 630-320-7139,

        &HEADLINE>Proper trainingis essential&/HEADLINE>

        All dock workers should be trained in restraint operation, and each new employee should get the same procedural instructions on the first day of work. Dock personnel should be offered incentives for reporting any malfunctions promptly, and should be warned that using restraints in an unsafe manner could result in disciplinary action.

        Training for truck drivers is also important. The company should send its trucking contractors a notice explaining the operation of the restraints, and copies should be kept at the dock area for distribution to others using the area.

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