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30 can be especially disconcerting to a very large, heavy-set States. According to Parker (1997), integrated safety belts were driver who is attempting to wear his/her safety belt com- much more comfortable for drivers, particularly for those rid- fortably. If during a bounce, or jostling around, the belts/straps ing on air-ride seats because in the older safety belt design, the cinch tight, this can become very bothersome to the driver, and belts were attached to the cab frame and rubbed the driver's it will warrant considerable driver complaints. person as the seat moved up and down. Proper installation of SIBs in the United States would require modifications to existent truck cab design to strengthen 7.4.3 Quick Egress from a Truck Cab the cab floor to support the SIB and seats would have to be in a Crash Sequence designed to withstand the loading throughout the seat frame One common reason for not wearing a safety belt given by itself (Clancy 2004, Sickon 2004). The requirements for seat truck drivers was their desire to have control over enacting a anchorage in Europe are only about half the strength require- "quick egress" from the truck cab during a crash sequence. ments of the U.S. market, and the design criteria for surviv- From a human factors and ergonomics perspective, there was ability of higher speed crashes must be more stringent. Proper a question as to how difficult that was or how time-consuming sled tests to verify design features and crash sequence charac- it was for drivers to unfasten their safety belts and extricate teristics would have to be accomplished. themselves from the cab. The research team did not find significant research data on 7.5.2 Safety Belt Tensioners this topic. Typically, when a driver wears a safety belt, it is not worn tightly around the waist and upper torso (shoulder straps). 7.5 NEW TECHNOLOGIES FOR TRUCK SAFETY BELT COMFORT During a crash sequence, it is important that the belts be AND USER-FRIENDLY DESIGN immediately tightened to start absorbing the driver's energy and slow down body movement (McNamara 1997a and b). Several new technological innovations are under consider- Therefore, another relatively new design feature under study ation for use in Class 8 truck seat and or safety belt designs. in passenger car safety belt design is the use of pre-tensioners Several designers of safety belts for trucks have worked on for safety belts to automatically take up the slack in a belt in user-friendly design features to make them more comfortable milliseconds at the moment of impact and thus couple the to use. For example, some safety belts are being designed with driver or seat occupant to the seat quicker during the crash a softer edge to the strap (belt) webbing or with different stitch sequence (McNamara 1997, Prentkowski 2004). One of the designs to provide better energy load limiting (Clancy 2004). important functions of pre-tensioners is to help reduce femur There have been experiments conducted on the use of electric load--the load one gets on the knees from being thrust into retractors for the excess material of the belt when the driver the instrument panel. They also provide additional protection permitted too much slack during use (Clancy 2004). Some in rollovers, because they keep the driver cinched down to the safety belt manufacturers are working on improving belt rout- seat. In those vehicles, the pre-tensioners are sometimes acti- ing and improving the latch-plate-to-buckle interface design vated by the same electronic sensors as those used for air bag (Sickon 2004). Some safety belt designers use a low-friction impact sensors (Prentkowski 2004, Gorton 2004, and Sickon D-ring for the belt to pass through on the wall anchor point, 2004). There are three types of pre-tensioners--retractor making the D-ring height adjustable. Some others are consid- pre-tensioners, buckle pre-tensioners, and lap anchor ering illuminated buckles to make them easier to locate in a pre-tensioners--that are being evaluated for transfer from crash sequence or at night (Sickon 2004). Insofar as they passenger cars to trucks (Prentkowski, 2004). involve additional ergonomics and human factors engineering principles, some of the technological approaches to subse- quent seat and safety belt design are outlined here. 7.5.3 Airbags and Safety Belts in Trucks Safety belts perform another valuable role by keeping the 7.5.1 Seat-Integrated Belts occupant properly positioned in front of an airbag during a crash sequence (McNamara 1997). This is becoming more Eventually, truck seat designers might work with those who important as more OEMs offer air bags in their heavy trucks. design safety belts to produce a safety belt system designed as For example, airbags can significantly reduce head injuries by an integral part of the seat assembly itself--the so-called Seat- preventing a driver who is wearing a safety belt from hitting Integrated Belt (SIB) design. SIBs are reportedly widely avail- his/her face on the steering wheel. able as a purchase option by OEMs in Europe, where a large Currently, installation of an air bag in front of the truck percentage of the large trucks are of the Cab-Over-the-Engine driver is available as an optional purchase on many of the (COE) design. This design is substantially different from the newer trucks. Such driver air bags are designed to inflate more conventional truck design commonly found in the United only in high-impact, frontal collisions. If a driver is wearing