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36 Guidebook for Implementing Passenger Rail Service on Shared Passenger and Freight Corridors informed by experience using the model, experience with interpreting the results, and experi- ence observing real-life outcomes. 3.2.2 Choice and Availability of Models This discussion focuses on appropriate models to support detailed negotiations with a host railroad to operate passenger train service over a busy rail corridor. The model used must be able to take into account all operating constraints and corridor features and must be accepted as pro- ducing valid results by all parties in the negotiation. Simpler or alternative models are often used during earlier planning stages and for corridors with less complex operations. In many cases, these requirements limit the choice to two comprehensive rail operations sim- ulation software packages that are widely used in the railroad industry for capacity evaluation and project and service planning. These packages have been used in almost all recent passenger rail service developments where corridor operations were sufficiently complex to warrant the use of detailed modeling. Some agencies may be uncomfortable with the apparently restricted choice of simulation soft- ware for capacity analysis and will point out that other models exist and have been used success- fully in the past. Although this is true, the firms responsible for the two leading software packages have continually refined their products, added new features, and built a broad user base among passenger and freight railroads. These efforts have given the models an industry-leading posi- tion, overtaking the competitors. In addition and most important, many passenger and freight railroads have invested considerable resources in assembling rail network infrastructure and operations data for use with their chosen package. It is costly and time consuming to re-input these data for use with another package, even if one were available and would be acceptable to all parties. The advantage of using one of the leading simulation models is that the results are highly realistic and are likely to be accepted as such by all parties. The long history of successful applications of the models to different corridors means that most potential "bugs" have been found and corrected, so the parties are very unlikely to encounter surprises when the new ser- vice starts operation. For these reasons, usually the most practical option regarding model choice will be to use the train operations software package routinely used by the host railroad to ana- lyze operations on the corridor. The two packages are Rail Traffic Controller (RTC) developed by Berkeley Simulation Software and RAILSIM developed by the rail consulting firm SYSTRA. RTC is specifically designed for application to North American freight railroads, with substantial unscheduled train movements and a range of signaling and train control methods. RAILSIM is most commonly applied to higher-density passenger rail and rail transit corridors and contains modules for modeling pas- senger car fleet utilization and other service design aids. In spite of this specialization, either pack- age can be applied successfully to passenger-dominant or freight-dominant shared corridors. The rail operations simulation models used by both packages are data-intensive and relatively costly to use. They require detailed information on track layout, speed limits, signal systems (including signal block lengths), and full details regarding the rail traffic operated. This detail includes data for each train or type of train operated, including locomotive or traction power and braking characteristics. The large amount of data needed, however, make these packages cumber- some and not well suited for use in earlier-stage planning studies or for the rapid screening of mul- tiple alternatives. Simpler models have been developed for this purpose, such as the Association of American Railroads Train Energy Model (TEM), a train performance calculator particularly designed to evaluate the effects of route characteristics and operating techniques on trip time and energy consumption. Also, several commercial consulting firms, such as Parsons Brinckerhoff and Zeta-Tech, have developed screening-level models for capacity and train performance analysis.