THE SCIENCE BEHIND THE SEAT
Why are there so many different seating designs on the market today – with such drastically different levels of comfort ? Most transportation seating solutions are designed for unique purposes . But even within the same application , why does Company A ’ s seat “ sit ” differently than Company B ’ s seat ?
The root reason is that all ergonomic design begins as
By Doug Oswald
an “ art form .” But the designers of the art form must take into consideration the application , dimensional , structural and production design criteria that uniquely shape the seat . At the same time , the designer has to create an ergonomic contour that will fit the widest range of all sizes of people . Since each transit seat is generally a common size , the ergonomic guidelines are to meet the needs of 5th to 95th percentile users .
All ergonomic design starts as an art form and takes shape through the application of the design criteria , but most of the science occurs in the evaluation of comfort . The following explains the science of ergonomic seating design .
Materials and processes
The application of new technology in materials and processes has always provided a significant impact on the history of product and seating innovation . The key in maintaining an ergonomic design is not to allow the production technology to overshadow the ability to achieve a comfortable seat . Too much focus on materials and processes that limit the three-dimensional contours of the seat is a recipe for a lack of comfort . Figure 1 shows two drastically different centerline seat profiles designed for the same purpose and meeting the same design criteria .
American Seating ’ s flagship product , InSight , was conceived , engineered , tested and tooled by American Seating to meet the needs of the North American heavy-duty transit market .
Ergonomically Correct , InSight Contour
Limited Contour , Production Focused Bus Seat
Dimensional and structural requirements
All bus seats are required to meet certain dimensional and structural
Figure 1 requirements , which impact the design of the seat . APTA guidelines specify certain dimensional standards in order to maintain seat sizes , angles and thicknesses , and each seat on the market generally complies . In addition , structural testing is done with static loading or dynamic force in order to prove structural properties for general durability and crash protection . While dimensional and structural requirements keep the seat design within some specific parameters , there are no specific ergonomic criteria that define the shape or comfort of the seat .
People size
The North American population has been getting larger for decades . Providing a seat frame and back with a slim profile and using curvature to enhance hipto-knee room are key to providing optimal comfort on a bus . Maximizing seat width is also critical to both comfort and personal space . Interior bus width and aisle space are set dimensions . Most seating manufacturers provide one size seat for all applications , but one
InSight ’ s slim profile and seat contour creates more space for enhanced ingress and egress and superior comfort .
Largest personal sitting area
Maximum aisle space *
* Maintaining White Book aisle space Figure 2
company offers two seat-width options : a straight-sided 17-inch-wide seat and an 18-inch-wide seat with a tapered upper section ( see Figure 2 ). This feature allows for maximum comfort while meeting industry dimensional standards .
Art ➤ Science
Although all ergonomic design begins as an art form , there is plenty of science that goes into a seat design . Once a look is established , understanding the physiology of comfort , and the science of how to create a comfortable seat , is critical . This is not to be trusted to designs from other continents , as body dimensions and comfort perceptions of the North American population are different than those of other countries . Utilizing a panel of people to evaluate how various body types interface with seating contours is part of solving the equation in ergonomic design development . This process is essentially trial and error until the optimal form is achieved .
InSight Seat Another Bus Seat
In addition to the seat contour , the pitch and
Figure 3 back angle of the seat play critical roles in comfort as well as retention in a moving vehicle . Digital pressure mapping is the latest technology to evaluate the comfort of a seat . While sitting upright on a flat surface , 75 percent of a person ’ s total body weight rests on two concentrated areas – technically referred to as “ ischial tuberosities ,” and known to most of us as the “ sit bones .” In the Figure 3 images , cooler colors represent less pressure ( absence of discomfort ) while warmer colors represent more pressure ( discomfort ). This technology is commonly used by those specializing in the science of seating , but there is a simple way a transit authority also can evaluate comfort scientifically . It is highly recommended that seating decision-makers establish a user panel and perform a survey to evaluate comfort of various seating samples .
Doug Oswald serves as the director of marketing for American Seating ’ s Transportation Division and has over two decades ’ experience in seating product development . Headquartered in Grand Rapids , MI , American Seating employs a U . S . -based workforce and takes pride in sourcing locally . American Seating has been listening to , designing for and investing in public transportation and related industries for 85 years . Flagship products InSight , Vision
® and Metropolitan
® were conceived , engineered , tested and tooled by American Seating
to meet the needs of the North American heavy-duty transit market . Visit www . americanseating . com for additional information .
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