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CHAPTER 7
ERGONOMIC AND TECHNOLOGICAL FACTORS
AFFECTING SAFETY BELT USE
7.1 BACKGROUND name safety belts are specifically requested to meet a cus-
tomer's special order.
This chapter focuses on ergonomic and technological fac- An ergonomic evaluation of safety belts must include sig-
tors that might affect driver choices to use safety belts. This nificant consideration of the choice of seats installed in the
section provides general background and perspective on the truck. Truck safety belts are mounted in conjunction with the
safety belts and how they are chosen for installation in com- particulars of each seat selected, because safety belt design
mercial vehicles. The following sections describe an ergonom- must interact with the particular seat a driver is using. Seat
ics assessment of current safety belt use, technological and design features of functionality, adjustability for best reach
human factors related to safety belt technology, evolving tech- of pedals and controls, visibility inside and outside the cab,
nologies in safety belts and user-friendly design, and conclu- absorption or attenuation of whole body vibration (WBV),
sions for consideration by the Partnership. overall ease of use of the seat, seat comfort, compatibility
The fundamental safety belt system in use in CMVs today with the safety belt design, and ease of seat care and mainte-
is a 3-point system that came about in the 1980s. In addition to nance, all are involved in the ergonomics and human factors
employing the usually expected driver-restraining lap belt, the considerations of selection, installation, and use of truck seats
3-point safety belt system incorporates a shoulder strap which and safety belts.
is fastened to the truck cab's "B-pillar" support structure above Because the ergonomics assessment in this study is pri-
and slightly behind the driver's left shoulder (see Figure 7). marily oriented to safety belts, the specifics of the many vari-
Through the 1990s, in an evolutionary way, the 3-point safety eties of Class 8 truck seats and the numerous human factors
belts underwent several design improvements. Since the mid- and ergonomics considerations of seats per se are only men-
1990s, 3-point safety belts have been adopted industrywide tioned here insofar as they have a direct impact on safety belt
and are now considered standard equipment. design factors.
Based on representation from six OEMs of commercial
trucks, it appears that 90% of the largest and principal fleet
trucks sold in the United States today are being equipped 7.2 ERGONOMICS ASSESSMENT
METHODOLOGY
and installed with safety belts manufactured by one safety
belt company. The precise market share of this manufacturer This section presents ergonomics and human factors engi-
was not independently verified for this study, but it is clear neering information as part of an assessment of the design and
that focus on this firm's product is valid for considering use of the safety belt systems more commonly employed in
ergonomic factors in the design of truck safety belts in the contemporary Class 8 trucks on the highways of the United
United States. States. Professional ergonomics standards, measurements, and
Product engineers and sales representatives of this com- seat evaluation guidelines (e.g., those established by C. M.
pany provided a technical presentation and demonstration of Gross et al. at the Biomechanics Corporation of America,
the design features and operation of their safety belts to the Melville, NY) (Gross 1996) were applied in the assessment.
Partnership meeting held at FMCSA in April 2004. Techni- The methods followed were (1) to conduct a literature search
cal and sales representatives also met with the research team of reports containing information on CMV safety belt design--
ergonomist for an interview session at the Freightliner Trucks in particular, to identify any human factors or ergonomics
facility in Portland, Oregon, in October 2004. studies of the safety belts; (2) to examine and conduct an
There are other safety belt products available, but they are ergonomics inspection of a variety of Class 8 truck safety belts,
found less frequently in the U.S. long-haul trucking industry. safety-belt-to-truck-seat combinations, or interactions among
Based on interviews with OEM representatives, the largest the seats and safety belts--to perform an examination of the
Class 8 truck manufacturers tend not to procure and install installation of safety belts in different varieties of Class 8
these other safety belts in trucks they sell, unless other brand trucks; (3) to interview and witness in operation a variety of
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discussion with OEM representatives on these topics. OEMs
contacted included Freightliner, Mack, International Truck and
Engine Corporation, and PACCAR (Peterbilt and Kenworth).
During a visit to one of the OEMs, the research team
ergonomist examined in-depth one particular new truck with
some of the latest optional safety belt features installed. An
on-the-road test ride and demonstration of the truck driver and
passenger seats, and the safety belts accompanying them, was
conducted as part of the ergonomics assessment. The truck
included a modern air-ride seat. The seating arrangement in
that truck included a 3-point safety belt (see Figure 8), com-
plete with two optional features designed to enhance driver
comfort in using safety belts: (1) a shoulder strap D-loop
height adjuster (see Figure 9) mounted on the truck cab's
B-pillar that permitted the driver to select about 7 in. of stroke
adjustment for shoulder strap placement to his/her preference
and (2) a shoulder strap equipped with a safety belt latch in
place that permitted drivers to insert an extra inch or two of
slack in the shoulder belt for added comfort as the strap
crossed the driver's chest (see Figures 10 and 11).
The 45-min on-the road demonstration ride included trav-
eling at varying speeds, enacting random forced quick stops,
driving around banking turns, roadway inclines and declines,
and driving over substantially bumpy roads, railroad tracks,
and so forth. In a truck static mode, ergonomic observations and
measurements were made with three drivers: a medium-sized
man, a large, tall man, a smaller-statured woman seated in the
driver's seat.
Figure 7. Three-point safety belt in a Class 8 truck. In addition to visiting several OEMs, the research team
also visited several truck carrier terminals and several public
CMV drivers who differed anthropometrically (body sizes, and commercially run truck rest stops in the states of Florida,
etc.) while the drivers wore or used truck safety belts; and Maryland, Oregon, South Carolina, and Virginia. At these
(4) to highlight some newer design technologies for possible locations, drivers were interviewed about their safety belt use.
subsequent application to safety belt installations in Class 8 The research team's structured interviews of CMV drivers
trucks. and of fleet managers (see Chapters 3, 4 and 5) included ques-
To study the different approaches employed in fielding tions about safety belt ergonomics and comfort issues that
Class 8 trucks, the research team ergonomist examined the could affect safety belt use.
interaction(s) of the 3-point safety belt with several alternative
air-ride truck seat designs, with different-sized drivers, and in
different kinds of truck cabs. The examination sampled about
a dozen different truck driver seats-to-safety-belt combinations
(i.e., different brands and models of trucks and different brands
and models of truck seats). The ergonomics assessment was
not an exhaustive one in that it did not include a comprehen-
sive assessment of the numerous truck brands and models and
seat brands and models available in the U.S. long-haul truck-
ing fleets.
The research team visited several OEMs to examine the
installation of current seat and safety belt designs and to study
differing approaches employed in fielding new Class 8 trucks
around the United States. The staff engineer at the Truck Man-
ufacturers Association (TMA) and a participant in the Partner-
ship (1) coordinated with several key OEMs to arrange visits
to their facilities to examine the installation of safety belts in
different brands and models of new trucks and (2) facilitated Figure 8. Safety belt viewed from lap connector.
