Presentation on theme: "Modeling Rail Capacity"— Presentation transcript:
1 Modeling Rail Capacity Rail Capacity DefinitionStringline DiagramsParametric ModelsTrain Performance CalculatorsTrain Dispatching SimulationAASHTO SCORT Sept 22, David Hunt of Oliver Wyman
2 Suggested Definition of Rail Capacity The maximum number of trains that can be moved between two locations in a day without exceeding a predefined level of service.
3 Elements in Determining Rail Capacity Line Capacity: number of tracks; type and spacing of control system; number, spacing, and length of sidings; mix of train types; operating and maintenance plansYard Capacity: total acreage; number of tracks; container storage slotsCrew Capacity: available crew starts; yard crews; maintenance crewsEquipment Capacity: locomotives; railcars; containers/trailersLine CapacityYard CapacityCrew CapacityEquipment CapacityThis presentation will focus on line capacity
4 Some of the Factors Determining Line Capacity Physical Track LayoutNumber of tracksType of signalsNumber and spacing of sidingsOperating PlanSchedulesType of serviceTrain makeupNumber and horsepower of locomotivesTrain length and weightGeographyMountainsTunnelsBridges
5 Maximum Versus Effective Capacity Transportation firms can never utilize a facility 100% of the timeMaintenanceWeatherPeaking of traffic volumesDisruptions and recoverabilityNormal variability in operational conditionsIndustry practices call for standards to maintain fluidity of operations and avoid major issues at chokepointsUseable (effective) capacity is 70% to 80% of the maximum (theoretical) capacityUtilizing the capacity buffer between effective and maximum capacity results in deferred maintenance, reduced ability to react to variability with increasing recovery time, significant reduction in reliability
6 Stringlines Graphical depiction of a timetable Provides a visual representation of trains scheduled to operate on a corridorTypically show stations (space) along the y-axis and time along the x-axisAlso referred to as time-space and time-distance diagramsHave many uses:Identification of schedule conflicts (meets/passes)Identification of slots for new serviceScheduling track maintenanceResource planning (crews, locomotives)
7 Transnet Freight Railroad: Witbank-Komatipoort Example StringlineTransnet Freight Railroad: Witbank-Komatipoort
8 Stringlines are a Primary Analytical Tool Used Worldwide Example from Kazakhstan Temir ZholyGreen & Blue = Passenger, Red = Freight, Brown = LocalsSoftware Products Allow:Selecting timeframes, corridors, and trainsBuilding or adjusting schedules by adding and dragging strings
9 Levels of Effort in Modeling Rail Capacity Initial EstimationPlanning ModelsSimulation“Back of the envelope” methodsExpert with basic knowledge of number of tracks, type of signals, and special conditions (e.g. mountainous terrain)Useful for quick assessment of a single corridor or facilityVariety of methods, requires more data than back of the envelope but less than a full simulationParametric (statistical based) models stem from 1975 FRA work and the CN model (Krueger, 1999)“Paper” simulations (now evolved to spreadsheets) are also used for capacity estimationUses a commercial rail simulation product (RTC, RAILS, FastTrack)Requires precise network layout (tracks, sidings, interlockings, signals, etc.)Requires knowledge of operating plan: trains that will be run and schedulesInitial setup is expensive
10 The AAR Approach to Modeling Rail Capacity National Rail Freight Infrastructure Capacity and Investment StudyRequested by the National Surface Transportation Policy and Revenue Study CommissionCommissioned by the AARPrepared by Cambridge Systematics, Inc.Purpose was to estimate the rail freight infrastructure improvements and investments needed to meet the U.S. DOT’s projected demand for rail freight transportation in 2035Used STB Waybill data, empty car estimates, and ORNL network attributes
11 AAR Study Recommended Levels of Service for Rail Source: AAR “National Rail Freight Infrastructure Capacity and Investment Study”, September 2007.
12 Forecasted Growth of Freight Trains Per Day 2035 – Based on US DOT Freight Analysis FrameworkSource: AAR “National Rail Freight Infrastructure Capacity and Investment Study”, September 2007.
13 Track Attributes Were used to Determine Capacity Type of Control SystemCTC=Blue, ABS=Green, Manual=RedNumber of TracksTwo or More Tracks=Blue, Single Track=TanSource: Oak Ridge National Labs rail network. Raw data not verified for accuracy.
14 Capacity Tables Used for AAR Study Tracks & ControlPractical Max w/Multiple Trains TypesPractical Max w/Single Train Type1 No signal16201 ABS18252 No signal28351 CTC30482 ABS53802 CTC751003 CTC133163Source: AAR “National Rail Freight Infrastructure Capacity and Investment Study”, September 2007.
15 Future Volumes Compared to Current Capacity 45% of Network at Level of Service E or FSource: AAR “National Rail Freight Infrastructure Capacity and Investment Study”, September 2007.
16 Parametric ModelingOne form of a parametric model:Where:C = maximum capacity in trains/dayN = number of tracksL = type of control system (categorical variable)S = average spacing between sidingsM = mix of train typesαi, βj = coefficients… other parameters may be consideredCalibrate model using:Capacity information for selected lines obtained from the simulation studiesC = β0 x (1 + β1 N)α1 x (1 + β2 L)α2 x (1 + β3 S)α3 x (1 + β4 M)α4 x …
17 Reporting Parametric Model Results Using AAR V/C Establish the level of service for each rail line:Where:R = volume to capacity ratio, from which the level of service (LOS) is determinedV = volume in trains/dayC = maximum capacity in trains/dayIdentify potential chokepoints:Lines with a LOS of “D”, “E”, or “F”, using the AAR capacity scaleOther special considerations (e.g. tunnels, bridges)R = V / C
18 Limitations of Parametric Models The Canadian National parametric model is the best known exampleIt was designed for single track corridorsDoes not handle complex track configurationsFRA has sponsored research into improving parametric models for more complex track layoutsParametric models are best used for high-level national or regional modeling to identify potential problem areasDetailed capacity analysis is done with simulation
19 What is Computer Simulation? Set of simplifying mathematical assumptions that attempt to duplicate actual train operationsThe simulation should allow a comparison of the current actual train operation with alternative assumptions about:Changes in the number of trainsChanges in the types of trainsChanges in the schedules of trainsChanges to the physical plant
20 Train Performance Calculator (TPC) The Physics of Railroading ObjectivesDetermine Minimum Run Time (unobstructed) on a specific route for specific train characteristicsDevelop run time information for use as input to dispatching simulation modelsEstimate fuel consumptionUsesProvides key component analysis for schedule preparationDetermines effect of line speed changes on run timeDetermines effect of train consist changesLocomotive (tractive effort characteristics, etc.)Cars (weight/braking characteristics, etc.)20
21 Train Performance Calculator InputsTrack profiles: Grades and curvesSpeed limitsTypical train and locomotive consistsOutputsUnhindered speeds and timesFuel consumption
23 Why do we use Train Dispatching Simulation Tools? TPC’s only provide the expected operational characteristics for a free-running train without regard to:Meets and passes with other trainsCapacity for schedule adherenceTrain prioritiesTrain density and characteristic mixPhysical plantMain track work
24 Train Dispatching Simulation Software Main objective: a mathematical approximation of operational results for a given set of variables based on a reasonable dispatching algorithmLogic attempts to realistically replicate decisions by a “good” dispatcher (not an optimal one)Other objectives:Reliable, repeatable resultsEase of useMinimize or automate input dataUser-friendly input proceduresComprehensive user interfaceExternally usable results
25 Event-Based Simulation Dispatching Attributes Dispatcher logicFollows rules - preferences - dynamic prioritiesMight lower the priority for high priority train running lateMight raise the priority for low priority train if crew close to exceeding hoursVariable - limited outlookAnti-lock-up logicAll moves tested before implementationWhen move is rejected, next most preferable move is selected
26 Dispatching LogicAcross each train’s look-ahead, conflicts are identifiedIf there are any, all “reasonable” resolution options are identifiedEach option for resolution is “costed” using user defined delay costs. These costs dynamical change as the simulation runs.Penalties are added for less preferred moves such as changing tracks, entering siding, etc.Options are sorted by “cost”Each option is submitted to the anti-lock-up logic until one is acceptedThe necessary moves of that option are implemented in the simulation
27 Train Dispatching Simulation Types of InputsInfrastructurePlantSignalsTrafficOperating characteristicsWhich trains are runningTrain prioritiesTrain size and powerRoute (including reverse moves if applicable)Time of operationSchedule based and non-schedule based
28 Special Routing Events Replicate track maintenanceRemove track/control point from serviceApply/remove temporary speed restrictionsReplicate train work at a locationTrain delay(s)Train characteristicsTrain connectionsReplicate passenger operationSchedule train(s) departure timesSpecify a route or track
29 Train Dispatching Simulation Types of OutputsStringline (time-distance plot)User configurable reportsTPC profilesTrack occupancy chartsAnimation of simulation
30 Individual train ”logs" Types of ReportsIndividual train ”logs"Scheduled & unscheduled delaysIn totalBy train typeBy locationStatistical analysesDistribution of trip timesLocomotive-milesDistribution of delaysUsed to determine if plant is balancedOperating costsTimetables
34 The Iterative Planning Process Using Computer Modeling Develop “base case” trafficTrack configuration, signals & other physical attributesOperating planDevelop alternative scenarios (changes to physical plant or operating plan)Compare alternative scenario to base, or to other alternative
35 The Iterative Planning Process Using Computer Modeling - 2 Inject track maintenance and operating failures at critical points, and determine if plant still works.If not, refine plant some more and re-runFirst without perturbationsThen with perturbationsSelect alternatives that meet operating objectivesIf none, refine alternatives & re-runBalanced plant is achieved when delays are evenly distributed
36 Limitations of Simulation Models Data and time intensiveMust validate to actualYard operations are modeled separately (hump operations, intermodal lifts, etc.)Resource constraints (crews, locomotives, etc..) are largely ignoredModels do not look beyond study area to the rest of the networkEven detailed simulation requires simplifying assumptions