CEM is a design concept that absorbs energy that is generated when a rail vehicle or a train consisting of several rail vehicles comes into frontal impact with another object. This design considers the longitudinal dynamics of the train, distributing collision energy among cars in a train consist. CEM rail cars can more efficiently absorb collision energy, as this energy is transferred to the front end of the locomotive, and to the following cars within the train. Key to the CEM design is the incorporation of a series of crushable elements into locomotive and car designs. In the event of a collision between a train of rail cars and another train or object on the right-of-way, the resulting vertical and lateral motions of the vehicles in the train are limited. Thus, coupled car interactions are controlled, and the saw tooth buckling and consequent overriding and derailment of the cars in the train can be successfully minimized. Most importantly, CEM maintains the occupant survival space and structural integrity of the locomotive and cars in the train. This reduces serious injuries and fatalities.
EU rail car designers have considered several scenarios during crash tests. These are also variables that are important within the United States parameters of weight and speed that were developed for each:
- Front end impact between identical trains.
- Front end impact between a streamlined passenger locomotive or rail car and a freight car with side buffers.
- Impact with a truck on a railroad crossing.
- Impact with a low obstacle on the right-of-way or a small auto on a crossing.
Passive Safety — Locomotive Cab Design
In the locomotive or operating cab car, the primary concern is the protection of the driver. In the event of a collision, the driver must be able to survive the initial impact, and have a means of escape. EU vehicle designers have been working on a monocoque cab construction design that will absorb the major stresses created as the result of the impact of a head-on crash.
The cab is designed with the driver's seat mounted on a platform. This platform moves under the extreme forces that are exerted in a collision. The seat is resultantly pushed away from the front of the locomotive toward the rear of the cab.
Special consideration has been given to doorways on the car body structure of the locomotive that lead to the engine room. These doorways provide a means of emergency egress for the driver, and have been re-enforced to ensure that frames do not buckle in the event of a collision. Doors can then be quickly and easily opened for escape. Designers are concerned about the opening motion of the doors, and have considered doors that can be opened in either the inward or outward positions. This will enable the driver to either pull or push the doors open quickly. This is a concern for designers, for the driver may either need to push or pull the door open. As an example, analysis indicated that the forces exerted upon the driver and door of a quickly braking train will make it virtually impossible for a driver to push a door against the direction of deceleration. The deceleration will make it easier to pull the door open. Also, there is a concern that damaged components in the engine room may make it impossible to push the door open. Pulling may provide the only alternative for a means of escape.
As noted earlier, the CEM designs are being tested for future construction of locomotives and passenger rail cars in both the EU and United States because it limits the deceleration rate, reduces the risk of derailment, reduces the risk of overriding (particularly on the front end of the locomotive) and maintains the integrity of each vehicle's car body structure, thus maintaining the survival space of the driver, other crew members and passengers.
Passive Safety — "Safe Train" and "Safe Interiors"
"Safe train" and "safe interiors" are projects through which EU vehicle designers have been working to enhance the interiors of passenger rail vehicles. Work is being conducted with the following objectives in mind:
- The preservation of survival space.
- The prevention of the intrusion of foreign objects from entering the passenger compartment, either from the under car section, the roof or the windows.
- Prevention of ejection of passengers through the windows or doors.
- Fire prevention. In the event of fire, inhibiting its spread throughout the compartment.
- Prevention and mitigation of passenger injuries while seated and standing.
- Escape aids in the event that passengers must evacuate for their safety.
Engineers within the United States have also looked at these variables, and have incorporated safer interior designs into the new Metrolink bi-level commuter cars.