Choosing the right vehicle restraint

The question used to be: Do we need vehicle restraints on our docks? Today, the more likely question is: Which kind should we choose? Dock safety has become top-of-mind. Company personnel now look at vehicle restraints as necessary safety devices. Vehicle restraints help prevent serious accidents that can happen when trucks or trailers separate from the loading dock while lift truck drivers are...


Key Concepts
  • Preventing trailers from separating from a loading dock is a major factor in dock safety.

  • Restraints are available to match nearly any kind of vehicle using loading docks.

  • The wide variety of available restraints can be classified into four major categories.

Solving a serious problem
Choosing the right restraint
Four categories of restraints
Handling special cases
More Info:

The question used to be: Do we need vehicle restraints on our docks? Today, the more likely question is: Which kind should we choose? Dock safety has become top-of-mind. Company personnel now look at vehicle restraints as necessary safety devices.

Vehicle restraints help prevent serious accidents that can happen when trucks or trailers separate from the loading dock while lift truck drivers are loading or unloading them. The restraint system securely holds the truck in place while providing communication that tells dock attendants when it is safe to load and tells truckers when it is safe to depart.

Vehicle restraints come in a variety of configurations, enabling plant personnel to choose a unit that provides a safe loading and unloading environment in almost any application. The trick is to choose the restraint that most cost-effectively fits the building, the loading or unloading operation, and the kinds of trucks being served. It's a decision to take seriously, because a restraint that fails to suit the application may do little more than provide a false sense of security.

Solving a serious problem

Vehicle restraints are important because the accidents they help prevent are often catastrophic. If a truck edges away from the dock or pulls out prematurely, a loaded lift truck and its driver may fall into the gap between the truck and the building. In some cases, the lift truck driver could be killed or permanently disabled.

Until vehicle restraints were invented in 1980, dock personnel tried to hold trailers in place using wheel chocks - typically, wedges of hard rubber placed under the rear wheels. Unfortunately, even when used properly, wheel chocks slip on snowy, icy, or wet pavement. They are also easily lost, stolen, or swept away by snowplows.

Furthermore, employees often neglect to use chocks. It is easy to see why, if one imagines an employee having to walk to a doorway, descend a flight of stairs, cross a driveway to the dock door, find the chocks, then bend down and place them beneath the wheels - sometimes in a downpour, oppressive heat, or bitter cold. Even with wheel chocks in place, trailers can separate from the dock in a variety of ways:

Premature departure. Wheel chocks cannot hold a semi rig under power. If a trucker pulls out while a lift truck is entering, backing out, or still inside, the lift truck driver is in serious jeopardy (Fig. 1).

Trailer creep. The impact and momentum of forklifts traveling in and out can cause the trailer to edge away from the dock until the leveler lip slips off the truck bed, opening a gap between the trailer and dock. With trailers that have air suspensions, the problem is more pronounced and is often called dock walk.

Landing gear collapse. A detached trailer spotted at a door may separate from the dock if the jostling of forklifts and loads causes the landing gear to buckle (Fig. 2).

Trailer upending. A forklift driven deep into a trailer may create an excess of weight toward the front end, causing the trailer to pitch forward on its nose. Similarly, an excess of weight at the rear of the trailer may cause the nose to pop up. A detached trailer also can separate from the dock if struck and tipped over by another truck.

Choosing the right restraint

Not every dock is vulnerable to every one of these accidents. However, a properly chosen vehicle restraint system can help prevent all of them. Most restraints hold trucks by grabbing the rear-impact guard (RIG); some engage the rear wheels. The exact method of restraint differs among makes and models.

To be effective, every restraint also needs a communication system of lights and signs that lets dock personnel and truck drivers know at all times whether the trailer is secured to the dock. In choosing restraints, it is essential to consider several factors:

  • Dock layout and height

  • Number of trucks serviced at each dock position per day

  • Types of trucks that use the dock

  • Need to service trucks with special or unusual configurations

  • Type and speed of material handling equipment; i.e., lift trucks, electric or manual pallet jacks, etc.

  • Loading conditions, such as weather

  • Budget.

    • Four categories of restraints

      The many kinds of restraints on the market break down into four basic categories. Each has its place, and some plants and warehouses are best served by using two or more kinds to meet specific needs at selected dock positions. Here is a look at the basic restraint choices.

      Manual vertical barrier restraint (Fig 3). These units, generally the least costly, can be mounted on the driveway, or above ground on the dock face, where the mechanism has less exposure to ice, snow, dirt and debris.

      To activate the restraint, a dock attendant reaches down with an operating bar and pulls the metal barrier device up into contact with the truck's RIG. This barrier keeps the truck from moving forward.

      These restraints are effective where the trucks being serviced are relatively uniform and have RIGs. They protect reliably against premature departure and trailer creep.

      Because these units are less effective against separation caused by landing gear collapse or trailer upending, they generally are not recommended for use with detached trailers. They are most suitable for smaller operations where employees can be supervised to ensure that they use the restraints consistently.

      Automatic vertical barrier restraint (Fig. 4). These devices are similar to their manual cousins, the difference being that the dock attendant activates the restraint by pressing a button. A hydraulic or electro-mechanical system moves the barrier into position.

      Easy to use, reliable, and simple to maintain, they work well in any setting from low-traffic operations to high-volume just-in-time and LTL applications that serve trucks with RIGs. They provide limited protection against landing gear collapse and trailer upending, but they have been applied successfully at facilities that service detached trailers in the context of strong policies requiring trailer jacks.

      Automatic rotating hook restraint (Fig. 5). These units are effective against all causes of trailer separation. Pushbutton-operated and usually mounted above the ground, they hold trailers with a steel hook that rotates up from a housing and wraps around the RIG.

      Once secured, the RIG cannot move away from the building, nor can it rotate to the side (as in trailer tipover) or ride upward (as in trailer upending). In fact, there are cases in which rotating hook restraints have held detached trailers upright when they otherwise would have fallen.

      Rotating hook restraints are durable and extremely flexible to accommodate RIGs of varying heights and configurations. As the truck backs in, its RIG contacts a spring-loaded housing that automatically positions it to the proper height.

      Automatic wheel restraint (Fig 6). The first three restraint categories are limited in that they cannot secure trucks that have no RIGs or that have special rear-end configurations, such as hydraulic lift gates, increasingly common on delivery trucks used in the food, beverage, healthcare, and other industries. Wheel restraints provide the ultimate in flexibility to secure trucks anywhere in the world, because they do not rely on a RIG. Instead, they directly engage the truck's rear wheels.

      Wheel restraints are effective against all causes of trailer separation. They retrofit easily to the driveway surface. A locking arm positions automatically, and with a simple push of a button, the truck's tire is engaged. There is no external power required. The restraint mechanism adjusts to different tire sizes to ensure firm engagement.

      Handling special cases

      One size does not necessarily fit all. For many facilities - especially those that serve trailers of uniform size and height with uniform RIG configurations - one variety of vehicle restraint may suit every dock position. But facilities that serve multiple trailer styles may be well advised to mix restraint systems.

      For example, a facility serving mostly standard over-the-road trailers but some lift-gate vehicles may benefit from outfitting one or two docks with universally flexible wheel restraints. A facility also may choose to install lower-cost vertical-barrier restraints for docks serving trailers attached to their cabs, and more sophisticated rotating hook restraints for docks serving detached trailers.

      The restraint selection process may appear complex, but the essential point is simple: Any plant or warehouse can have a vehicle restraint system that effectively protects employees against trailer separation accidents - and does so at a reasonable cost.

      Loading dock equipment manufacturers' representatives can help in the selection of a restraint system that meets the daily demands of the operation and provides a safe work environment.

      More Info:

      Walt Swietlik is available to answer questions regarding vehicle restraints. He may be contacted at xxx-xxx-xxxx or zzz@xxxxxx. Article edited by Richard L. Dunn, executive editor, 815-236-2196, or .

Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
September 2018
2018 Engineering Leaders under 40, Women in Engineering, Six ways to reduce waste in manufacturing, and Four robot implementation challenges.
GAMS preview, 2018 Mid-Year Report, EAM and Safety
June 2018
2018 Lubrication Guide, Motor and maintenance management, Control system migration
August 2018
SCADA standardization, capital expenditures, data-driven drilling and execution
June 2018
Machine learning, produced water benefits, programming cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
August 2018
Choosing an automation controller, Lean manufacturing
September 2018
Effective process analytics; Four reasons why LTE networks are not IIoT ready

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Material Handling
This digital report explains how everything from conveyors and robots to automatic picking systems and digital orders have evolved to keep pace with the speed of change in the supply chain.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Design of Safe and Reliable Hydraulic Systems for Subsea Applications
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
click me