Equipment

Human Factors: Blind Spots in Heavy Construction Machinery

Driving a loader safely requires different skills and equipment than other common vehicles.
By Udo Schultheis
April 20, 2022
Topics
Equipment

Articulated loaders, excavators, rollers, and cranes are important construction tools and have been upgraded and improved with new technologies like 3D animations, load weighting and much more over the last couple of years. Unfortunately, statistics show that construction workers still suffer every year in a high number of non-fatal and fatal incidents (e.g., approximately 800 fatal accidents according to the U.S. Bureau of Labor Statistics for 2019) due to contact with these types of machines. Most accidents happen when machines or vehicles like loaders and trucks are moving in reverse and ground workers or pedestrians are near the rear of these machines .

Safety requirements for constructions machines and dump trucks have been developed as a part of “lessons learned” initiatives over many years (for instance, use of reverse signal alarms and others), are specified in International Standard Organization and other standards and in some cases are required by OSHA. Additionally, in the last couple of years manufacturers of construction, forestry and mining equipment adopted technologies already introduced in other fields like the automotive industry.

Machines like heavy articulated loaders have been equipped with rearward and/or sideview cameras; other common object detection technologies like radar, lidar and ultrasound are going to be added in ongoing initiatives to improve safety. Thus, ground workers as well as pedestrians around and especially behind machines should be detected by this technology and made known to the operators on screens in the cabins of the machinery.

Construction contractors accept the extra costs associated with such technologies as worthwhile investments in efficiency as well as safety. Safety technology should increase productivity as operators are warned of proximal objects and work more efficiently, with less stress induced by the operator’s fear of hitting someone. Additionally, fatal incidents can be prevented or reduced. A fatal accident on a construction site can be followed by weeks of investigations and force a construction site to halt work, resulting in the loss of millions of dollars.

In the passages that follow, the use/tasks of a loader, specifically, will be examined under the magnifying glass of human factors to find explanations for accidents. Hintze et. al. (2005) noted that human factors is involved in virtually all accidents on constructions sites.

Blind Areas

Due to the nature of heavy machinery’s size, intended use, design, feasibility and productivity, operators of construction machines have only limited sight beyond their cabins. The blind area behind the machines, therefore, presents a significant problem when moving backward.

One solution to the blind area problem, already used for many years, is to support operators with several inside and outside cabin mirrors.

In another solution, the heavy equipment industry listened to the voice of the customer (VOC) demanding, basically, “a rearview camera system as is already found in modern passenger vehicles.”

In the United States, camera-based rear visibility systems are mandatory for vehicles manufactured on or after May 1, 2018. This is based on the Cameron Gulbransen Kids Transportation Act published in the Federal Motor Safety Standard No. 111 (FMVSS 111). FMVSS 111 resulted from an incident in which a parent backing up his SUV through his driveway used the side and rearview mirrors, as well as looking over his shoulder, to try to prevent hitting anything. Sadly, his child happened to be in a blind area behind the SUV, was run down and died instantly. The supposedly “safe” SUV turned out to be unsafe, and a subsequently long legal battle led to the need for rearward facing camera systems, ultimately transforming the law. Rearview camera systems evolved from optional accessories into standard safety measures.

Currently there are plans to either fully or partly replace conventional mirrors with “smart” camera-based mirrors (a camera monitor system [CMS]). Aside from providing an expanded field of view, it is assumed that CMS’ real benefit would be presenting real-time video on a centralized monitor in the cabin (possibly “stitched” together with videos from other areas around the machine). The intent is to save the operator time and effort (rather than constantly turning his or her head to different mirrors) by conflating all images into one. Other benefits include automatic adjustment to reduce glare or increase brightness at night. Drawbacks of the system are the dependency on additional software, the addition of another system in the machine that can potentially fail and the fact that the conventional mirror is always presenting the “real situation” at that time.

On a first view, the above-mentioned technological advancements seem to be a logical solution—why not mount a video camera on the back of a construction machine, feed the video stream to a monitor inside the cabin, thus solving the blind area problem?

The Driving Task Compared Against the Task of a Loader

Experienced drivers may no longer realize it, and novices must learn, practice, and get used to it—the task of driving a car is a complex instrumental activity with a constant challenge of interacting with rapidly changing variables of an environment. The main driving task is keeping a vehicle on the road. Other tasks include changing lanes and/or passing another car. The driving task is versatile and includes either forward or backward movements. Backing up a vehicle is necessary when driving out of a parking stall, for instance, at the grocery store, or backing up or into a driveway or a garage. The task is complex, includes a combination of directional and speed inputs from the driver combined with obstacle avoidance and spatial positioning.

A rearview camera presents a video of the situation with a specific field of view (sometimes over 180 degrees, depending on type and make of the vehicle), the position of the rear bumper, and (typically selectable) trajectory lines indicating the movement of the vehicle depending on the input to the steering wheel. Inside the car, on the upper part of the middle console, a video screen is presented as a part of the entertainment system (the term “entertainment” is actually a misnomial relic referring to when radios were placed at this position), and the driver can theoretically fully focus on the screen when backing up (despite a warning is presented on nearly all screens on the market indicating that the driver is still responsible for checking the surroundings of the vehicle). Extended rearward movements with cars are rather rare.


Two examples of rearview camera images with trajectory lines.

A loader is a heavy machine mainly used for moving earth, gravel, rocks and other construction material from one position to another, usually from a stockpile to a dump truck or to another location on a dump yard. Most commonly, a loader is operated in a “v-shape” or “short loading cycle” (SLC). During an SLC the operator’s main task is to move the bucket of the loader to either fill it or empty it. The operation of a loader is an extremely complex dynamic task requiring continuous concentration of the operator on the position of the loader and, most importantly, the three-dimensional position of the bucket. This is combined with applying the adequate speed control (e.g., when driving the bucket into a stockpile to fill it), the speed/kinetic energy of the bucket needed to get into the stockpile, the approach of the dump truck and the raising of the bucket. Additionally, the loader operator needs to get the job done quickly to enable operational productivity.

The 10 phases of a loader SLC loading material like sand, gravel, rocks etc. from a stockpile on a dump truck. The longer the loader needs to drive backwards, the longer it takes to fully load the truck as the V-shape turns in a Y-shape positioning (adapted from Frank, Kleinert and Filla, 2018).

When comparing the backward driving task of a car and that of a loader, it looks as though the rearview camera could be used to satisfactory effect in either situation.

However, a closer look into the human factors of operating a loader reveals a different slant. Wallmyr (2017) used eye tracking technology to identify the areas of attention of a loader operator during a loading cycle. Results indicate that the major focus of the operator was toward the front, ahead of the loader. Furthermore, little attention was recorded through the side windows and the rearview mirrors, even while reversing. Interestingly, a rearview camera monitor placed on the lower right of the loader’s cab was not viewed by the operator during the session being analyzed with the eye tracking technology.

Conclusion

The driving task of a driver in a common passenger vehicle is significantly different from the task of a loader operator and that equipment supporting the driving task in a car cannot applied in the same way in a loader. Furthermore, the installation of rearview cameras cannot solve the blind area problem of a construction machine like a loader. Until technological solutions can be found to suit, for instance, a loader operator’s unique situation, we will have to continue relying on more conventional safety measures.

by Udo Schultheis
Dr. Udo Schultheis is an expert in Psychology and Human Factors associated with personal litigation, commercial and passenger land, air, and water vehicle accidents, safety and personal protective equipment, product failure analysis, warning and alarm signaling, and labeling.

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