Several years ago, the Federal Railroad Administration (FRA), with assistance from the Volpe National Transportation Systems Center, began conducting research and testing to develop strategies for enhanced passenger protection in the case of train accidents. The key strategy is crash energy management (CEM) that can significantly improve structural rail car crashworthiness. It also included enhanced interior features, like safer workstation tables and seats for commuters.

Metrolink, the commuter rail authority in the Los Angeles region, is the nation’s first commuter rail system to adopt the resulting state-of-the-art features for cab and passenger cars, including important collision-absorption technology. A fatal collision in Glendale, Calif., in January 2005 provided the impetus for incorporating this advanced technology in equipment Metrolink was at the time in the process of procuring. The accident took 11 lives when a cab car-led train ran into a locomotive-led freight train after it hit an SUV parked on the tracks and derailed.

In February 2010, Metrolink took delivery of the first two of 117 CEM-enabled cars. They were built by Hyundai Rotem in South Korea in a $230 million procurement. The remaining cars will continue to arrive from South Korea over the next year with shipments to be completed by spring 2011. In accordance with the “Buy America” program, final assembly will take place at Metrolink’s new Inland Empire Eastern Maintenance Facility (EMF) in Colton, Calif. The assembly work will create nearly 60 local skilled jobs. Metrolink is currently testing the first two “pilot” cars and the Southern California Regional Rail Authority will start placing the cars into revenue service in fall 2010.

Crashworthiness

CEM improves crashworthiness with crush zones at the ends of the cars. These zones are designed to collapse in a controlled fashion during a collision, distributing the crush and absorbing the energy among the unoccupied ends of the train cars. This technique preserves the occupied spaces in the train and limits the deceleration of the occupant volumes.

To achieve this, the crush zones are required to absorb several million foot-pounds of energy and deform gracefully as they crush, minimizing vertical and lateral car motion and preventing override. The crush zones are unique to each end of the Metrolink CEM cars, but share common elements. For instance, the pushback coupler mechanism is designed to absorb energy and has a sliding sill with shear bolts. As the first point of contact, the coupler absorbs crash energy and helps keep cars in line and upright. All cars have structural endwalls to protect the passenger compartment.

The coupler is composed of a standard elastic element that functions in normal service. When normal loads are exceeded (i.e. contact at speeds more than 5 mph) for the coupling, a tube within a tube crushes to absorb energy and keep the cars in line. At collision speeds greater than 12 mph, the coupler absorbs energy until the endframes of the cars come in contact. Once the endframes are in contact and activation loads are reached, a sliding sill with shear bolts is activated to allow the carbody crush zone to be activated. The sliding sill keeps the endframe aligned during the crushing of the collapsible mechanisms. The pushback coupler mechanism could be fitted on existing cars, but may require redesign and modifications to the structure so the cars will support the new coupler system.

Crush or compression zones include LTM PEAM (load transfer mechanism and primary energy absorption mechanism) and compression tubes. These devices absorb, balance and dissipate energy away from the passenger occupied area. The non-cab upper absorbers are collapsible components in the crush zone energy absorption system. The non-cab end crush zone is located on the outside of all normally occupied space and the end frame is located at the extreme end of the car.

The upper absorbers are square “tubes” composed of several cells that collapse in a controlled manner and stay aligned to provide graceful deformation while absorbing energy. They are an integral part of the carbody structure design and thus cannot be retrofitted into existing cars. The LTM PEAM is the same concept, but with tapered tubes that allow the cells to be activated in a progressive manner with slightly more force as they work their way from the front cells to the back ones. Tube within a tube members such as that used for the push back coupler are also used in the underframe to absorb energy.

The engineer is located in the elevated train engineer compartment at the upper level. This location enhances visibility while providing added protection in case of a grade crossing collision with a vehicle.

Performance Testing

How well does the CEM technology perform in actual testing? In 2006, the FRA conducted full-scale, comparison testing of both existing passenger rail trains and ones fitted with newly developed cab and coach car crush zone designs. This testing was conducted as part of a larger testing program to establish the degree of enhanced performance of alternative design strategies for passenger rail crashworthiness, including crash energy management. By controlling the deformations at critical locations, the CEM train is able to protect against two very dangerous modes of deformation: override and large scale lateral buckling.

In a train-to-train crash test with a closing speed of about 30 mph with CEM equipment installed, the front of the cab car crushed by approximately three feet, and the crush propagated back to all of the unoccupied ends of the trailing passenger cars.