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9 In one study, an attempt was made to improve seat design as common to this research project as they were to the Balci methods and processes and to capture the effects of seat dyna- study. mics on ride quality. Hix, Ziemba, and Schoof (2000) sug- gested that since air suspension seats used in trucks isolated a 2.6 DRIVER DEMOGRAPHICS significant amount of the road vibration, it was critical the seats be designed so that the driver experienced a good ride A self-reported data study focusing on potential impacts from the seat. Hix et al. evaluated two different seats: (1) a of driver demographic characteristics (Shinar, Schechtman, typical North American air-ride seat which had thick-soft and Compton 2001) found through its analysis that observing foam, a parallelogram vertical suspension, and a pendulum speed limits, not drinking and driving, and wearing a safety type fore/aft isolator and (2) a typical European seat which belt were safety behaviors that were entirely independent of had thin-firm foam, a scissor-type vertical suspension, and a one another. Furthermore, the study found--contrary to certain spring-type fore/aft isolator. stereotypes--that income, education, and age were not deter- To accomplish a thorough modeling of truck seats, Hix et al. minants of safety behaviors. The only predictor found was that accounted for numerous measurements of several obvious female drivers are more likely to follow all three safety com- seat components (seat cushions, riser base, air springs, shocks, ponents of this study. shock absorbers, fore-aft isolators, nuts, bolts, bearings, etc.) and of a number of seat design features (including vertical per- formance and fore/aft compliance). As part of their project, 2.7 EFFECT OF LAWS Hix et al. also chose to evaluate safety belt comfort. They did their physical tests on a 5-degree of freedom seat-shaker table, Cohen and Einar (2001) concluded that safety belt laws upon which they measured such characteristics of seats as applying to all drivers did lead to an increase in safety belt accelerations, displacements, forces such as force-deflection usage, and thus an increase in lives saved. It also drew a com- splines (stiffness), and constant damping coefficients (for parison between primary and secondary state safety belt laws. vibration attenuation). The researchers concluded through their analysis that if all Hix et al. intended that the forces measured validate com- states moved toward a primary enforcement policy, national fort variables of the full occupant restraint systems (safety rates of safety belt use would increase 9% to 77% and 500 belts). However, their work in taking measurements of both lives would be saved annually. seats found the forces to be small; and the safety belt retrac- tors they tested never experienced "lock-up." They con- 2.8 OVERVIEW OF AUTO SAFETY cluded the safety belts did not have any adverse effects on BELT PROGRAM comfort during any of their normal test ride (shaker table) events. Therefore, Hix et al.'s seat models did not include The research team also considered the significance of the the entire restraint system, including the retractors (Hix efforts and success of the NHTSA's earlier initiative to et al. 2000). increase safety belt use by automobile drivers. Although fac- In 2001, Balci, Vertz, and Shen conducted a questionnaire tors relating to safety belt use by CMV and passenger car driv- survey regarding safety belt comfort and usability. Signifi- ers are different in some respects, the information about the cant findings in this survey indicated that five problems were NHTSA effort can provide a baseline and starting point for persistent among automobile drivers. This research showed future efforts to promote increased CMV driver safety belt use. first that two of these issues were (1) that the safety belt was A detailed report of the NHTSA program is included as difficult to negotiate with clothes and (2) that the belt would Appendix E of this synthesis. It outlines the phases and pro- get caught in the door. These were not found to be common grams associated with increases in safety belt use from 1978 to complaints among those CMV drivers who answered the 2003. The appendix describes the approaches used to increase research team's questionnaire. Three other complaints, belt safety belt use, including public information, education, incen- twisting, belt lock-up, and difficulty locating the buckle, were tives and rewards, requirements (laws), and enforcement.