# A Review of Seatbelt Technologies and Their Role in Vehicle Safety
## 3 Results
### The Pretension System
Pyrotechnically activated pretensioners can be the following:  
Figure 8: The ball-in-cup inertial locking mechanism. 1. Piston and cable type--which act on the third anchor point of the belt, known as the PLP (Pyrotechnical Lap Pretensioner). They act on the sharp that passes through the abdomen (pelvic) area, reducing the distance between the occupant and the seat back; 2. Piston and cable type--which acts on the belt buckle, also known as PBP (Pyrotechnical Buckle Pretensioner). It acts mainly on the diagonal strap that passes over the occupant's chest and to a certain extent on the lap strap, providing correct positioning during a collision; 3. Ball and profiled sector type--RRP (Rotational Retractor Pretensioner)--which acts by winding the strap on the retractor reel; 4. Wankel type--which acts by winding the strap on the retractor reel; 5. Piston and rack type--which acts by winding the strap on the retractor reel. The types of pyrotechnically activated pretensioners are presented in Figure 9a-e.  
Figure 9: Pyrotechnically activated pretensioners: (**a**) piston and cable type; (**b**) piston and cable type with action on belt buckle; (**c**) ball and profiled sector type; (**d**) Wankel type; (**e**) piston and rack type. A pretensioner can also be reversible, using electric motors, adjusting the belt tension according to the situation to improve safety and comfort. These systems, which we call pretensioners, can be activated even before impact, for example, during sudden braking, preparing the passenger for a possible collision, as also mentioned in [21]. The authors in [22] discussed the effect of pretensioner force on the human body. Two different retractor pretensioners with varying pretensioner force were used in the crash test for a child and an adult passenger positioned on the rear seat. Head displacement and neck loading were reduced for both pretensioners for all dummies compared to testing without a pretensioner. The pretensioner reduced chest deflection to the adult but not to the child when seated on a booster cushion with a back during the crash phase. When the back was removed, chest deflection was reduced below injury assessment reference values. The head excursion was reduced for all dummies with both pretensioners. According to [23], a seatbelt pre-pretension system can reposition forward-leaning passengers, increasing safety in the event of a crash. Also, ref. [24] investigated the muscle responses of passengers during autonomous braking events with reversible pre-tensioning. They showed that average muscle activity with a pre-tensioned belt increased rapidly before the onset of deceleration for females, but not for males. A study using active human body models (AHBM) for female occupant kinematics and muscle activations in vehicle maneuvers potentially occurring in precrash situations and with different seatbelt configurations was conducted in [25]. For specific muscles, lane changes with the pre-pretensioner belt result in earlier muscle activation onsets and significantly smaller activation amplitudes compared to the standard belt. Another study by [26], using the active SAFER human body model (Active SHBM), notes that the presence of Automated Emergency Braking (AEB), type of seatbelt system, pre-pretensioner activation time and force can affect the ability to reposition the passenger body on front seat and time required. In case of rear collisions, Ref. [27] mentions that seatbelts and pretensioners were designed for occupant restraint in frontal crashes, so it is not a surprise they do not provide much restraint of an occupant in rear impacts up to 40.2 km/h (25 mph). The lack of early lap-belt restraint is due to the unfavorable belt angle from the anchors over the hip.