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44 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide LRV designs and feature multiple articulated carbody sections, and partial or full low floor design. While some of these new vehicles were designed mainly for railroad operation, several smaller models have been conceived to allow city street operation. Like the LRV, the light passenger rail car offers several different modes of propulsion. Features Preferred for Shared-Track Operations Certain key systems and capabilities exert an overriding influence on vehicle performance and suitability for shared-track duty. Other subsystems such as heating, ventilations, air condition- ing (HVAC), doors, lighting and interiors, are common to nearly all rail cars and have little influ- ence on shared-track. 1) FRA Compliance The main focus of the requirements for vehicle crashworthiness specified in 49 CFR Part 238 is to protect the integrity of the vehicle structure in the event of a collision with another rail vehi- cle. While these requirements make FRA-compliant car bodies more resistant to collision forces, the vehicles are also relatively heavy, and the design flexibility to adapt the vehicle for differing service applications and operating environments is more limited. This is exemplified by the range in weight per seat of North American DMU products. Research showed that FRA-compliant DMUs are 63% heavier on a per seat basis than noncompliant ones, and approximately 25% of the vehicle weight is structure. Part 238 also addresses equipment and interior attachments, elec- trical safety, fuel storage, emergency lighting, and other matters. Other requirements are set out in 49 CFR Part 221 (Rear End Marking Devices), 49 CFR Part 223 (Safety Glazing Standards) and 49 CFR Part 229 (Locomotive Safety Standards). They estab- lish lighting conspicuity and other vehicle requirements. Since deviations will be scrutinized by the FRA, they should be limited to significant components or structural elements where feasibil- ity, cost, or performance is negatively impacted. Noncompliance will have to be explained, and justified from a safety perspective. 2) Crash Energy Management (CEM) While an FRA-compliant rigid car body can withstand a high impact force, if it has no means to absorb and dissipate collision energy, the impact on the occupants will be higher. Crash energy absorbing devices can provide a measure of protection to the train and most importantly to the passengers because the equipment is designed to control the rate, location, and extent of gross car body crush and thereby lower the deceleration forces experienced by the train occupants dur- ing a collision. This CEM approach has been exhibited recently by FRA demonstrations at Pueblo, CO, and also by the Safetrain project in Europe. The benefits of CEM can be envisioned by comparing falling on an ice rink to the experience of falling on grass. Energy absorbing devices serve better than a FRA-compliant rigid structure to cushion the passengers inside the train from bearing the full impact force of a collision. This phenomenon has been noted in a number of National Transportation Safety Board (NTSB) Railroad Accident Reports. Another method of protecting commuters is to provide a large volume unoccupied by riders as a sacrificial zone in the rail car, or multiple strategically placed voids to absorb crash energy. A disadvantage of this approach is that it impacts car capacity. The majority of carbuilders now incorporate some sort of crash energy management features (as shown in Figure 4) on their multiple unit (MU), and LRV vehicles, aimed at mitigating hazards to train crew and passengers in the event of a collision. These devices fall into three primary categories. Each device is designed to absorb incrementally higher impact force loads,