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CHAPTER 3 Analysis and Modeling 3.1 Introduction Negotiating access to a rail corridor for a new or expanded passenger rail service often raises highly technical questions about rail line capacity, the extent and nature of capacity investments required, providing service reliability and planned journey times, estimating capital and operating costs, and determining how costs should be divided between multiple rail corridor users. In corridors with rel- atively simple operations, these questions can be answered by manual analysis (for example, using string charts) or exercising simple train performance models. However, in corridors with complex operations, either high-density traffic or operations with many long-distance and unscheduled freight trains, these questions cannot be answered by simple analyses or using a negotiator's per- sonal experience. Instead, the negotiators need to rely on detailed analyses using the different kinds of models to resolve these questions. Modeling methods and model inputs must be acceptable to all parties to ensure that the results are trusted and can be used to guide the parties toward an agree- ment. It is generally not productive for each party in the negotiation to perform its own analysis and compare results. Experience has shown that the results from different models are rarely identical. They can differ enough to cause disputes about the validity of the models for the specific situation being analyzed--the unproductive "dueling models" situation. This situation can add to negotiat- ing difficulties rather than guide the parties toward a mutually acceptable agreement. The specific areas where detailed analysis and modeling may be used include: Operations simulation and capacity analysis. Capital cost estimating and cost sharing. Operating costs and cost sharing Amtrak avoidable-cost methodology. Fully allocated costs for commuter rail. The following sections discuss analysis and modeling techniques used for passenger projects and how they have been applied. 3.2 Operations Simulation and Capacity Modeling 3.2.1 Simulation and Modeling Overview Except for the simplest of operations, there is no easy formula that will yield the capacity of a rail corridor. There are simply too many variables involved (train characteristics, speed limits, train and siding lengths, signal system characteristics, etc.) for any simple approach to yield use- ful results. Because of this level of complexity, all methods of operations simulation and capac- ity analysis rely on detailed operations simulation methods. 33

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34 Guidebook for Implementing Passenger Rail Service on Shared Passenger and Freight Corridors Simple Models In its simplest form, a simulation model is a computer program that performs a stepwise cal- culation of the movement of a train over a rail corridor. Using information on speed limits, grades, train acceleration and braking rates, station stop dwell times, etc., the model calculates the speed and distance traveled by the train for each time step (e.g., every 10 seconds). After the model has stepped along the whole corridor, it produces a tabulation of time and distance traveled, often presented graphically as a time vs. distance string-line chart. A model that performs this calcu- lation for a single train moving over a rail corridor is usually known as a Train Performance Calculator (TPC), because it calculates travel time without interference from other trains oper- ating on the corridor at the same time. TPCs often have additional features, such as an ability to calculate energy used or fuel consumption. Single-train TPC calculations are used to determine what rail corridor upgrades will be required and to provide the desired travel time before the interference effects from other trains and other typical operating delays are taken into account. For initial planning, it is customary to pad the minimum trip time by around 10 percent to esti- mate a practical trip time. This type of calculation can be used to investigate such questions as the reduction in journey time from increasing top speed from 79 mph to 110 mph, or adding or omitting station stops. Complex Models The more complex version of a train operations simulator performs a simultaneous calcula- tion of all train movements on the corridor, taking into account signal system characteristics, train priorities, temporary slow orders, and typical dispatcher decisions over where trains should meet or overtake each other. At their most complex, the multi-train simulations closely reproduce how a real rail corridor would be operated, taking into account all the variations in individual train performance and other operating constraints and variations. Results are usually presented as the calculated trip time for each train compared with minimum time with no interference from other trains, slow orders, etc. The difference is reported as a delay. Operation over the corridor can also be represented on a string-line chart (see Figure 3-1) or as an on-screen animation-- a speeded-up version of a dispatcher's display. However, a single run of a corridor operations simulation will only represent operations under one set of input conditions. Railroad operations are subject to a variety of random and planned disruptions to normal operation, including planned and unplanned track maintenance, delays at stations, and delays caused by events elsewhere on the railroad. Freight train operations are not normally conducted with great precision, and even scheduled freight trains are subject to variability. In addition, many through freight trains are unscheduled "extras" that run as needed and may enter the corridor at any time. Multiple model runs are used to address these variables, with results presented as average run times and delay statistics for each train, along with string charts and animations as required. The primary use of a multi-train simulation model is to investigate which infrastructure upgrades to an existing rail corridor are needed to enable it to accommodate additional passen- ger train trips while still meeting specified service performance requirements (train departure times, trip time, and on-time performance) and complying with any other specified constraints. The analyst will start with improvements identified using a single-train TPC (if available) and will make multiple model runs to test alternative track configurations and other improvements. The objective is to identify a cost-effective package of improvements that will meet the service requirements of all users. Given the trial-and-error process of using simulation models, the com- plexity of these models, and the potentially large number of alternative corridor configurations to be investigated, an experienced modeling analyst is essential. Modeling is something of an art, and a model cannot represent everything about a route. Interpreting results requires judgment,

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Sunday Monday (Day 0) (Day 1) Tuesday Wednesday (Day 2) (Day 3) Note: Trains 1-6 are passenger and the remainder are freight. Source: UVA IDOT Base Case report for the FRA Figure 3-1. String charts for different days of the week on a segment of the Chicago to St. Louis corridor.