CHAPTER 1

Introduction

The objective of this project was to create an easy-to-use toolkit for predicting the long-term safety and health performance of bus operator workstations. The toolkit helps assess the effects of operator size and shape, workstation geometry, and vehicle technologies. These assessments are performed through a process called virtual fit testing (VFT), where thousands of virtual users’ interactions with the bus operator workstation is simulated.

The success of designs intended for human use is determined by a wide range of factors, such as safety, aesthetics, effectiveness, portability, and cost. Although one factor may be the driving force for a specific design, the impact of each factor requires a significant amount of research and is its own field of study (11). Through theoretical analysis and practical experiment, researchers explore how each factor contributes to the overall outcome. As many industries become more transparent, companies are evolving to meet shifting needs; among these are user-centric elements such as human variability.

1.1 Design for Human Variability

Design for human variability (DfHV) considers the inherent variability in the target user population during the creation of designed artifacts. Several factors influence this variability, including when and where someone is born, cultural background, family atmosphere, and religion (12). Other factors such as sex, race, ethnicity, and age can dramatically impact how humans act, react, and interact (13). DfHV is the practice of designing artifacts, tasks, and environments that are robust to the variability in their users. This requires clearly defining the user population and understanding attributes that affect their interaction with the design.

1.2 Anthropometry

Anthropometry, one of the major fields of research in human variability, is a systematic and statistical study of the measurements and proportions of the human body. A combination of these measurements and proportions describes the size and shape of a human body, which makes individuals unique (14). There are many ways to categorize anthropometric variables. One common way is to distinguish them as length-related variables, such as stature, trochanter height (leg length), and hand length, and width-related variables, such as hip breadth, calf circumference, and chest breadth. Intuitively, taller people are expected to be wider than their shorter counterparts. This inference is usually true; however, there are exceptions due to human variability. For instance, the width of a human body is not only an indicator of its size, it can also be a measure of obesity. In this case, body width is independent of body length. Therefore, careful consideration is required to choose the most appropriate anthropometric indicators while making design decisions.

Anthropometry is commonly considered in industrial practice; anthropometry-focused concepts can be found in vehicle packaging, furniture designs, sport equipment innovation, and clothing design. The expectation of this practice is to achieve a greater outcome while minimizing cost so the final product is effective yet efficient. A poorly designed product can cause discomfort and dissatisfaction in users and result in a decrease in productivity (15). In certain circumstances, it can even put users in life-threatening danger. Thus, designers must diligently study the anthropometry of a target population and use the associated artifacts to guide their designs.

1.3 Accommodation

A good design should accommodate its users so they can perform the required tasks without encountering limitations (3). When a user is accommodated, they will feel safe and comfortable doing physical tasks, which can increase their productivity. In contrast, when a user is disaccommodated—they are unable to interact with the artifact, task, or environment in their preferred manner—their job satisfaction level is generally low, and the likelihood of safety hazards increases significantly (16). In many cases, companies and designers invest resources to achieve a better accommodation level. Practically speaking, perfect accommodation usually does not exist. When designing for a large audience, it usually costs a tremendous quantity of resources to accommodate the users with extreme body dimensions; as a result, companies tend to target the majority rather than all users.

Although most designs are not expected to accommodate every user in the target population, there are times when it is necessary. In competitive indoor and outdoor activities, sports equipment is frequently custom-made for best performance (17). For instance, NBA players are known for their elite performance on a basketball court. Competing with other extraordinary athletes, it is a significant advantage to jump a little higher or change direction a little faster. This pursuit of excellence inspires top shoe companies to take 3D scans of professional athletes’ feet and analyze the loading condition on their shoes to design shoes specific to the athlete that enhance their performance (18, 19, 20).

Customized designs can sometimes maximize the performance of a product, but they usually raise the cost significantly. They not only require more design considerations, but also bring challenges to the manufacturing process (17). For instance, many plastic products are formed through injection molding, which is a process of melting and injecting material into a mold. Due to the dimensional precision of the molds, they are expensive to produce. With machine testing and labor cost, it is difficult to justify the cost when only a small quantity of parts is needed (21). Alternatively, additive manufacturing saves on tooling, but requires additional research and time. Because of its layered nature, it may lead to structural failures (22).

1.4 Body Dimensions

Human bodies vary significantly in size and shape, which creates a difficulty in providing universally functional solutions for a population. One of the common approaches to resolve this issue is to create various sizes of a product and let users or retailers determine which size is most suitable for each consumer. Shoes are a great example of this strategy (23). In the United States, shoe sizes are typically designed in increments of 0.5 or 1. With help from the elasticity of the materials, these increments are small enough to accommodate most users (24). One of the greatest advantages of this approach is its simplicity; however, it is not suitable when users desire different sizes. Another approach to accommodating variability is to implement adjustability in product dimensions. For instance, a belt allows the user to adjust the tightness of it around the waist. Instead of having to purchase belts of various sizes, the user only needs one

adjustable one (25). However, the major disadvantage of adjustable components is the increase in complexity of a system, which can cause a higher failure rate (26). An adjustable product also frequently involves a higher part count, which often means higher cost (16).

Analysis of anthropometric data has shown that many anthropometric measurements can be approximated as normal distributions, especially length-related ones, with the majority of the data clustering in the middle and the extremity of the data spreading at the tails (27). In product design, it is neither economical nor realistic to accommodate 100% of the user population due to the large spread of body dimensions. Thus, a design usually aims to accommodate a proportion of the user population (15). In practice, a target percentage of accommodation is preselected, 90% for instance, and serves as an assessment goal for the final product. Users who are disaccommodated can sometimes still achieve compromised comfort by adjusting their posture.

In other cases, however, disaccommodation may lead to safety hazards. Such phenomena exist throughout the world but are more common in developing countries because resources are more limited. Agriculture plays an important role in northern China’s economy, and large machines are used to reduce the amount of manual work. If a worker has a difficulty operating these machines due to physical limitations, the probability of injury is much higher. In fact, a study observed a 13.1% prevalence of machinery-related injuries from the surveyed agricultural workers due to machine sizes and other limitations (28). A similar point can be made in vehicle interior design. Failure to reach the instruments to operate a vehicle or inability to maintain an adequate field of view are associated with car accidents (29). Therefore, designers and engineers must ethically investigate the consequences of disaccommodation before making design decisions.

1.5 Postural Preference

Human interaction is not only impacted by the physical dimensions of the human body but also by a user’s postural preference. Postural preference is unique and can be dramatically different from person to person (30). For instance, the purpose of a chair is to provide a sturdy seating surface that supports the user. However, the action of sitting is very complex. Given a standard chair, some like to lean backward, some like to cross their legs, some prefer to sit high, some do not use the armrests (31). Assessment of success is no longer limited to the fundamental purpose of a chair, but rather the capability to accommodate the postures of as many users as possible to provide the most comfort.

Collecting data on postural preference can be a costly process because it requires user participation, which involves experiment design, user testing, data collection, and user feedback. In many cases, the size of a testing group is critical to an unbiased solution. With a small testing group, extreme behaviors are sometimes magnified and can be overanalyzed, which can lead to biases (32). The testing group must also represent the actual user population in terms of demographic descriptors, such as male-female ratio, age, race, and ethnicity. Thus, doing market research in preparation for any postural experiment is essential (33, 34).

Occasionally, postural preference can be transferable across products when the two products are used in a similar way, but careful consideration needs to be given to the risk of oversimplifying the problem (35). For example, ice skates and running shoes are comparable in shape and are worn similarly, but they serve different purposes. Ice skates must be stiff enough to protect users from twisting their ankles, but running shoes need to provide shock absorption and comfort, which is why new products usually need to run their own user interaction experiment. Unlike interaction preference, physical dimensions of a human body usually only need to be measured once. These dimensions can be simulated in space using software to display results in dimensional fitting (36).

1.6 Vehicle Packaging

The knowledge of spatial dimension and postural preference is useful in many fields of design, especially vehicle packaging. As defined by Roe, vehicle packaging is a subject that studies a vehicle’s interior spacing and components layout for the purpose of providing safety, spatial accommodation, and comfort to drivers and passengers (27). Of all the components inside a vehicle, the two most critical in this work are the steering wheel and driver’s seat, because they determine the driver’s capability to operate the vehicle (37). By the definition of accommodation, drivers must be able to adjust these two components without encountering any limitations to comfortably turn the steering wheel and step on the accelerator pedal or the brake pedal. One other consideration is driving safety (3). While operating a vehicle, drivers must maintain awareness of the surrounding traffic to make proper decisions (8). The goal of vehicle packaging is to scientifically design vehicle layouts to accommodate driver anthropometry so that both spatial fit and driver field of view can be achieved.

1.7 Research Overview

Driving trucks and buses is a physically demanding occupation that carries one of the highest injury rates of major occupational categories in the United States. Drivers often work in postures that increase risk of low back pain and other musculoskeletal disorders, slow their response time, and put them at increased risk for acute injuries due to crashes. Poor exterior visibility for drivers also increases the risk to other drivers, pedestrians, and workers. This report investigates bus cab spatial layouts and considers the effect of bus drivers’ body dimensions and postural preferences.