Crashworthiness Requirements for Commuter Rail Passenger Seats

Abstract

Occupant experiments using instrumented crash test dummies seated in commuter rail seats have been conducted on board full-scale impact tests of rail cars. The tests have been conducted using both conventional cars and cars modified to incorporate crash energy management (CEM). Test results indicate that an improved commuter seat design could significantly reduce occupant injuries associated with collisions of CEM railcars. Commuter seats built to specific crashworthiness design requirements can mitigate the increased severity of secondary impacts associated with CEM equipment. In a collision, the leading car or two in a CEM consist may have a more severe longitudinal crash pulse than the leading car in a conventional consist. The crash pulse associated with a leading CEM cab car results in a higher secondary impact velocity between the unrestrained occupant and the seat, when compared to a conventional cab car. This conclusion applies to both rear- and forward-facing occupants. As a result, the seat must absorb more energy, which may cause significant deformation of the seat back, preventing occupant compartmentalization. Compartmentalization is an occupant protection strategy that aims to: contain occupants between rows of seats, provide a ‘friendly’ impact surface, and prevent tertiary impacts with other objects. To compartmentalize occupants during a collision, seats must be relatively stiff. To limit the forces and accelerations associated with occupant injury, the seat must be compliant, absorbing the occupant’s kinetic energy as it deforms. The objective of seat design crashworthiness requirements is to strike a balance between the competing objectives of compartmentalization and minimizing occupant injury. Work is currently on-going to design, build and test a prototype 3-passenger commuter rail seat that will improve interior crashworthiness. The first step is to develop the design requirements, which are based on a head-on collision between a CEM cab car-led train and a CEM locomotive-led train. The seat design will be evaluated using quasi-static and dynamic finite element analysis. The occupant response will be evaluated using a collision dynamics model two rows of seats and three Hybrid III 50th percentile anthropomorphic test devices (ATDs). The seat design will be modified until the analytical models demonstrate that it meets the design requirements. Finally the prototype seat will be fabricated and tested quasi-statically and dynamically to ensure that the seat meets the design requirements. This paper describes the performance-based requirements that the prototype commuter rail seat must meet. Performance-based requirements include occupant compartmentalization, maximum allowable injury criteria, and maximum allowable permanent seat deformations. The paper also provides strategies for designing commuter seats that are better able to manage and dissipate the energy during a secondary impact. The paper describes computer models used to determine if the seats meet the design requirements.