This Is AuburnElectronic Theses and Dissertations

Seat Belt Safety in Rollover Accidents: Investigating Buckle Release Force and its Impact on Occupant Protection




Nageswaran, Shivaprasad

Type of Degree

PhD Dissertation


Industrial and Systems Engineering


Seat belts have been a crucial safety feature in vehicles for over a century. They undoubtedly remain the most effective safety device in a vehicle for reducing both fatal and nonfatal injuries resulting from motor vehicle crashes when used correctly. However, the persistence of high numbers of road transportation crashes and fatalities worldwide necessitates continued efforts to improve vehicle safety. Despite numerous safety and technological advancements, in the United States, motor vehicle accidents continue to be a leading cause of death for people aged 1–54, and the leading cause of work-related fatalities. Over the past two decades there has been an increase in belted fatalities with more than half of all fatalities being belted. Additionally, rollover accidents, which account for 30% of all fatalities and are the most fatal motor vehicle accident in the U.S., are on the rise. Current seat belt buckle standards require that a force of no more than 133 N be applied for the buckle to release. This standard threshold has not been modified since its inception in 1965 and is more than double the requirement of European and Australian standards. Given the rising sales of SUVs, prevalence of obesity, use of pretensioners, and rise in belted fatalities in the U.S., it is imperative to examine the adequacy of existing seat belt standards, reconsider certain standards, and explore opportunities for improvement. In addition to the use of seat belts in cars, the issue of seat belt usage on school buses has been a topic of debate in recent years, with growing advocacy for their installation. The lack of seat belts raises concerns over the ability of children to unlatch them in emergency situations. This is particularly concerning in the case of school buses, where the driver may be the only adult present, leaving children responsible for their own safety. Concerns exist regarding situations in which individuals may be inverted and are unable to release their seat belts, including both passenger vehicles and school buses. The research conducted in this dissertation aimed to address important gaps in the existing literature by exploring two critical elements. Firstly, it investigated whether adults can safely unlatch a motor vehicle seat belt in a rolled-over position. Secondly, it explored the design of seat belts for children on school buses, and their ability to operate and unlatch them in the event of a rollover accident. The research involved two primary studies and was split into four experiments. The first experiment measured the force that adults (18 years and older) could exert on a seat belt buckle in different orientations (0°, 90°, 180°, 270°). The second experiment evaluated their ability to unlatch a seat belt in different rolled over orientations (90°, 180°, 270°). The third experiment recorded the strength capabilities of children (5 – 16 years) to exert force on a seat belt buckle in both upright and rolled over orientations (90°). The fourth experiment evaluated their physical capabilities to unlatch a seat belt buckle in both orientations. The findings of this dissertation suggest that while the majority of adults were able to unlatch seat belts in different orientations, they were not able to exert the force of 133 N required by existing seat belt standards. Additionally, around 13% of children were unable to unlatch their seat belt in a rolled over orientation and none of the children were able to exert a force of 133 N. These findings suggest the need to reconsider and reduce the maximum force required to unlatch seat belt buckles in order to improve safety standards. The study provides valuable insights into potential areas for improvement in seat belt design and safety standards. It highlights the need for future research in developing new seat belt standards and evaluating the capabilities of children to unlatch seat belts on school buses in emergency situations.