Questions about using the longitudinal static strength (buff strength) of light-rail vehicles (LRV) as a means of controlling vehicle crush and protecting passengers in a collision remain unsettled and have prevented consensus on a structural safety standard for LRVs. This issue is clearly illustrated by the large differences between U.S. and European guidelines; on average, European cars are built closer to a 1-g buff strength while U.S. cars are customarily 2-g.
The U.S. 2-g guideline has a long history and was developed prior to the availability of computerized engineering analysis that can simulate structural crush performance of rail vehicles. Computer simulation tools are now used by railcar manufacturers to better understand vehicle crush behavior and to incorporate new design philosophies that control structural crush using a technique called Crash Energy Management (CEM). How buff strength is related to dynamic crush behavior of the vehicle and ultimately to passenger safety has not been sufficiently understood to establish an acceptable structural safety standard for LRVs that departs from traditional guidelines. This uncertainty also affects a transit agency's ability to freely choose between U.S. and European vehicle designs and be sure of their safety.
CEM design that is incorporated into an LRV may also provide added protection to passengers in roadway vehicles during collisions with LRVs. Accident statistics for U.S. LRV operations, as revealed in a recent survey by the American Society of Mechanical Engineers (ASME) Rail Transit-1 (RT-1) Committee and its CEM Subcommittee, indicate that collisions of LRVs with roadway vehicles result in a significant proportion of all injuries and fatalities associated with LRV operation. Installation of a CEM design on the leading end of LRVs may reduce the frequency and severity of roadway vehicle passenger injuries, but it is not clear how effective or practical CEM may be for this purpose.
The ASME RT-1 Committee and its CEM Subcommittee have been working to develop a structural safety standard for LRVs. Considerable effort has been expended to understand the complicated issues associated with the myriad of LRV designs and operations. The committee has determined that a concentrated effort is necessary to reach final agreement on an acceptable structural safety standard.
To further assist with the ASME RT-1 effort, research was needed to establish crush performance requirements that could serve as the principal part of a potential ASME structural safety standard, specifying levels of crush force and force-displacement relationships based on engineering analyses and simulations of various accident scenarios. These requirements would take into account variations in the operating environment, train consist configuration, occupant-compartment protection, and variations in current and anticipated vehicle designs. In addition to crush performance requirements based on LRV-to-LRV collisions, this research will assess the effectiveness and practicality of using LRV CEM structural design approaches to mitigate roadway-vehicle passenger injuries resulting from LRV collisions with roadway vehicles.
Developing a structural safety standard based on contemporary CEM technology could lead to advantages such as more competitive vehicle pricing, reductions in accident claims, reduced weight, and lower operating cost, making LRV travel more cost effective. Passenger safety would also be improved by reduced deceleration forces and better control of vehicle crush. In addition, CEM technology could provide better protection for the passengers of roadway vehicles that experience collisions with LRVs. The incorporation of crush zones and the establishment of CEM principles would also allow for better compatibility with lighter vehicle designs from Europe.
The primary objective of this research was to provide technical assistance to enable the ASME RT-1 Committee and its CEM Subcommittee to determine reasonable performance requirements for dynamic crush behavior for LRV-to-LRV collisions based on a CEM approach that minimizes the probability of injury and fatality for a range of LRV designs under various high-risk collision scenarios. As a secondary objective, the ASME RT-1 Committee and its CEM Subcommittee sought information and guidance on the technical feasibility and practicality of CEM zones to mitigate damage and human injury in roadway vehicles during LRV-roadway vehicle collisions. This research supports the current ASME RT-1 effort to develop an ASME structural safety standard for LRVs.
The research determined through engineering analyses (e.g., computer simulations) the relationships between crush behavior and the risk of occupant injury and fatality over a range of possible LRV designs and LRV-to-LRV collision scenarios. Suggestions were provided for defining vehicle dynamic strength requirements. The research used non-linear, dynamic computer modeling to estimate the LRV-to-LRV crush behavior and the buff strength of several current LRV designs to assist in understanding the implications of considering a change in design requirements from static strength to CEM.
Status: The revised final report has been published as TCRP Web-Only Document 40.
