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27 Figure 9. Shoulder strap D-loop height adjuster. Figure 11. Shoulder strap tension adjustment mechanism (latched). 7.3 RESULTS OF ERGONOMICS ASSESSMENT the 20th to the 80th percentile anthropometrically). However, In general, the professional opinion of the research team it is the research team's view that the design of universally ergonomist is that safety belts being installed in Class 8 used safety belts does not serve well the population of large, trucks appear to be practical and functional. The belts effec- heavy-set, obviously obese drivers. Additionally, the shoul- tively serve a large portion of CMV drivers (approximately der belt may rub or chafe the necks of small-statured drivers. These two design problems with the CMV safety belts are addressed in more detail in this chapter. It seems clear that over the past decade, industrial design and ergonomics work has been focused on making the over- all design of safety belts user friendly, incorporating flexibil- ity in facile ease-of-use design attributes, driver comfort features, and appropriate user-fit considerations. New safety belt designs include two features to make the placement of the lap belt and shoulder strap more flexible by (1) allowing for shoulder strap height adjustments on the B-pillar to accommodate larger or smaller drivers through installation of a shoulder strap D-loop height adjuster and (2) permitting the driver to adjust the amount of belt and strap tension and pressure, particularly of the shoulder strap against the driver's chest and upper torso through use of a shoulder strap tension adjuster. However, most of the trucks examined during this ergonomics assessment either did not Figure 10. Shoulder strap tension adjustment mechanism have these new features installed, or in many of the cases (unlatched). where they were installed, the drivers did not appear to use
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28 them. In some cases, it was obvious the drivers did not ited few "wear and tear" markings normally indicative of know how to use them until shown by the ergonomist. repeated use. The observation of a lack of understanding about how to use safety belts was found to be true in general through- out the interviews of approximately two dozen drivers. 7.3.1 Instruction on Care and Maintenance Thus, in addition to convincing drivers to regularly use of Safety Belts their safety belts, it is apparent that more training on the The safety belt installation and user manual that the research proper use of the safety belts as they were designed to be used team observed provided ample instruction and guidance on may be an important issue as well. how drivers should use, care for, inspect (every 20,000 miles), and maintain their safety belts. Some OEMs incorporate por- 7.3.4 Physical Characteristics of Truck Drivers tions of these instructions directly into the actual new truck Using Safety Belts owner's driver manual issued when a new truck is purchased. Upon delivery of every new truck, a few OEMs also provide a Some driver complaints regarding safety belt features are VHS video tape illustrating operation and maintenance of the attributable to the huge variety of physical characteristics of new truck; and these tapes also include proper safety belt the driver population (e.g., trying to accommodate a wide instruction. variety of anthropometric and biomechanical considerations of the driver population itself, that is, big drivers and small drivers). The ergonomics assessment notes that very large 7.3.2 Driver Complaints with Safety Belt Features drivers, particularly very tall and heavy-set drivers, and those with very large waistline and chest measurements, are likely Several past surveys (e.g., Balci, Vertz, and Shen 2001) to have difficulties in comfortably using any 3-point lap and reported truck drivers complained that their safety belts got shoulder belt design. Additionally, small-statured drivers, trapped in the cab door, twisted, cinched, or locked up; they particularly less than 30th percentile drivers, will have diffi- found the buckle difficult to operate, requiring two hands to culties with the 3-point belt systems. fasten or open; or safety belts were difficult to locate to put on For very heavy-set, "large-bellied" drivers, it is very diffi- or take off. Drivers claimed safety belts were difficult to cult to properly position the lap belt as recommended by safety manipulate or to wear, especially with heavy winter clothing belt designers: "2 to 4 inches below the waist, low on the lap, on; or they complained the belt pulling was not smooth; or the against the thighs, and tight against the hips--but never wear- belt became loose and slack over time; or the shoulder belt ing it over the abdomen or stomach." Such placement of the slipped off the shoulder. The research team found similar lap belt below the large stomach would cause the belt mate- issues in the literature review and in field interviews. In dis- rial to "cut" into the skin, the waist, and the abdomen; and cussions with the research team, drivers complained that the undoubtedly it would be quite uncomfortable. Properly worn belts (lap and shoulder) rubbed or chafed their skin, waist, shoulder straps are supposed to cross the collarbone and fit shoulder, and neck. snugly between the breasts. The research team ergonomist wit- The research team ergonomist witnessed some of these nessed evidence that some larger drivers and some smaller complaints. However, the research team's ergonomics assess- drivers had troubles with proper, comfortable placement of the ment found no obvious safety belt design features that con- shoulder belt as well. tributed to or made many (but not all) of these complaints a The small-statured driver must contend with additional reality on a regular basis (day to day usage). The research team anthropometric compatibility issues. It is challenging for a did observe that some drivers did not know how to use safety small driver to properly adjust most of the air-ride seats so that belts properly or how to take care of and maintain their safety he/she can comfortably reach the controls (especially pedals, belts. Both situations were encountered in this evaluation. gear shift lever, radios, instrument panel knobs) in the cabs of some Class 8 trucks. Therefore, selection of a seat for the small-statured driver is an important consideration. 7.3.3 Need for Training in Proper Use of the Truck Safety Belts During an interview with an OEM design engineer, a small-statured woman (5 ft. 2 in. tall and 120 lbs) who also Truck drivers gave numerous reasons for choosing not to was a CDL holder, questions were raised about various wear their safety belts. Many of those reasons were highlighted ergonomic factors of seat and safety belt design as they in the results of fleet manager and driver surveys in this syn- affected small drivers. Before driving on the road, the small thesis. During the ergonomics assessment, the research team driver set the adjustable controls of the driver's air-ride seat ergonomist, while interviewing CMV drivers seated in their for needed positioning fore-aft and for height, and set the trucks, encountered several instances where the drivers seem- safety belt and shoulder strap for preference. Then as the ingly had little actual experience using or wearing their safety woman explained, while driving over rough, bumpy roads, belts. In some cases, safety belts (even in rather used trucks) railroad tracks, and so forth, a certain amount of jostle and were hung neatly along the B-pillar, but the belt material exhib- bounce would be experienced. This could have a disconcert-