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.
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.
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.
The controlled deformation of the cab car prevented override. All of the crew and passenger space was preserved. In contrast with existing equipment, the colliding cab car crushed by approximately 22 feet. No crush was imparted to any of the trailing equipment. Due to the crippling of the cab car structure, the cab car overrode the conventional locomotive. The space for the operator’s seat and for approximately 47 passenger seats was destroyed.
In the two-car test of conventional equipment, the conventional car crushed by approximately six feet and lifted about nine inches as it crushed. In addition, the coupled cars sawtooth-buckled, and the trucks immediately adjacent to the coupled connection derailed. In the two-car test of CEM equipment, the cars preserved the occupant areas and remained in-line, with all of the wheels on the rails.
In the single-car test of conventional equipment, the car crushed by approximately 6 feet, intruding into the occupied area, and lifted by about nine inches, raising the wheels of the lead truck off the rails. Under the same single-car test conditions, the CEM trailer car crushed about three feet, preserving the occupied area, and its wheels remained on the rails.
Since many commuters use work tables while riding, the new Metrolink trains feature tables that dissipate the force of a collision. The tables were developed through a cooperative agreement between FRA and the Rail Safety and Standards Board (RSSB) in the United Kingdom. Metrolink and Hyundai Rotem, using the results of this research, designed tables that could be manufactured and were practical for use in the cars. The table top is about two inches thick with a honeycomb core that functions as a stable surface in normal service. In the case of a collision, the table edge crushes to absorb the impact and dissipate it across a wider surface that is in contact with the passenger’s midsection.
Passengers ride in comfortable seats, with higher seat backs for enhanced safety. When stopping suddenly the distance passengers travel after a collision can contribute to injuries. By limiting the space between seats, there is less injury due to secondary impact velocity (SIV), while having higher seat backs prevents passengers from going over the seat in front of them.
In a collision, the lead car experiences greater deceleration than subsequent cars. In a Metrolink CEM cab car leading configuration, the passengers in the cab car seat face rearward so there is no distance for the body to travel as it is already in contact with the seat back. In the trailer car the seats face both directions, but there is less effect as the trailer car would be at least the second car back in a train behind a cab car that had already absorbed the initial impact.
Other safety features on the new Metrolink CEM cars include illuminated and marked pathways and exits and emergency pull away windows for easier access should a crash occur. The new cars are fitted with inward and outward facing surveillance cameras in the operator’s compartment. Other surveillance cameras throughout the cars continuously monitor the train environment for passenger safety.
The Metrolink CEM cars’ stainless-steel exterior requires no paint to protect the environment and employees. Another “green” feature is the central air/heating that uses non-ozone depleting R407c refrigerant. Other amenities for passengers in each car includes a bathroom, drinking fountain, power outlets and storage area for bikes and strollers. Of course, cars are fully accessible to persons with disabilities.
The Metrolink CEM cars will also be fitted with positive train control (PTC), a computerized safety system to prevent train-to-train collisions. Metrolink has been granted $21.3 million in federal stimulus money to install PTC in accordance with the agency’s accelerated strategy to bring this technology to Southern California. The PTC system prevents collisions by automatically enforcing speed restrictions. PTC is designed to prevent accidents like the severe collision between a Metrolink train and a freight train in September 2008 that claimed 25 lives and injured more than 130 people when a train driver crossed through a red light. The collision resulted in making it mandatory for most America railways to install a PTC system by 2015.
Ideally, the whole menu of CEM technology should be designed into new equipment for optimum safety improvements. However, there are benefits to installing some of these safety features when overhauling existing equipment. For example, a conventional cab car-led train of single level equipment with end vestibules can protect all of the occupants in a collision with a locomotive-led train of the same weight for closing speeds up to approximately 15 mph. Switching to a CEM cab increases this safe closing speed to 25 mph. Retrofitting trailer cars with conventional carbody structures with pushback couplers can increase this closing speed to 28 mph. According to FRA and Volpe researchers when new equipment is purchased, it should first replace existing cab cars with CEM cab cars. After the conventional cab cars are replaced with CEM cab cars, the coach cars can be replaced with CEM coach cars.
Bill Siuru is an automotive journalist in Temecula, Calif.