# A Review of Seatbelt Technologies and Their Role in Vehicle Safety
## 3 Results
### Interconnection of Active and Passive Safety Systems  
The interconnection between active and passive safety systems has become over the past years a cornerstone of modern vehicle safety design, ensuring full occupant protection by dynamically adapting to various driving scenarios. Passive safety systems, such as seatb belts and airbags, serve as fundamental protective measures during a collision. However, the integration of active safety features has significantly enhanced their effectiveness by preemptively responding to potential hazards. Figure 11: Seatbelt mechanical components. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Position** & **Mechanical Function** & **Electronic Function** \\ \hline \multirow{3}{*}{Retractor} & \multirow{3}{*}{Bottom of the seatbelt near the reel (B-pillar)} & Inertia-sensing device (pendulum or flywheel) & Crash sensor \\  & & \begin{tabular}{c} Spool with ratchet teeth \\ \end{tabular} & & \begin{tabular}{c} (accelerometer) \\ \end{tabular} \\  & & \begin{tabular}{c} Locks when vehicle decelerates or tilts \\ suddenly \\ \end{tabular} & & \begin{tabular}{c} Signal sent to solenoid to \\ lock the spool \\ \end{tabular} \\ \hline \multirow{3}{*}{Pretensioner} & \multirow{3}{*}{\begin{tabular}{c} Within retractor \\ housing or buckle \\ assembly \\ \end{tabular} } & \begin{tabular}{c} Pyrotechnic or spring-based piston \\ Pulls on belt spool or buckle via cable \\ Instantly removes slack during crash initiation \\ \end{tabular} & \begin{tabular}{c} Connected to airbag ECU \\ Triggered milliseconds \\ before airbag deployment \\ \end{tabular} \\ \hline \multirow{3}{*}{Lad Limiter} & \multirow{3}{*}{\begin{tabular}{c} Inside retractor \\ mechanism \\ (spool shaft) \\ \end{tabular} } & \
\begin{tabular}{c} Torsion bar or deformable metal \\ Allows controlled payout under high load \\ Reduces chest force by gradual release \\ \end{tabular} &
\begin{tabular}{c} Typically passive \\ Some adaptive systems \\ may use actuators for \\ real-time control \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical and electronic functions. In a crash event, sensors detect rapid deceleration, then the pretensioner activates, pulling the belt tight in milliseconds, and then the retractor locks, preventing further movement. The presence of the load limiter slightly releases tension to reduce chest injury. In Figure 12, a type of seatbelt is illustrated which is designed for enhanced crash safety, automatically tightening upon detecting a possible collision, or in different dangerous situations. This type of motorized retractor with an electronic pre-pretensioner is common in modern vehicles for adaptive safety features and can also integrate with AEB systems. One innovative approach to this integration involves smart seatbelt control systems equipped with sensors embedded in seat structures and vehicle flooring. These sensors detect seat occupancy and passenger positioning, ensuring that the vehicle remains immobilized unless all occupants are properly restrained, thereby reinforcing seatbelt compliance as a precondition for vehicle operation [38]. Smart seatbelt control systems in modern automotive applications are designed to enhance occupant safety by integrating sensors, electronic control units (ECUs), and adaptive mechanisms that respond to real-time conditions. Unlike traditional passive seatbelt systems, smart seatblets can preemptively tighten or adjust restraint force based on data such as vehicle speed, braking force, seat occupancy, or crash prediction algorithms. A prominent example is the Mercedes-Benz PRE-SAFE system [39], which detects emergency braking or skidding and automatically pre-tensions the seatblets before a collision occurs, reducing slack and positioning occupants optimally for airbag deployment. Similarly, BMW's Active Protection System [40] activates pre-crash seatbelt tensioning when it detects an imminent accident via forward-facing radar or camera systems.