The Public Transport program is the CUBE Voyager program that lets you prepare public transport data and model public transport systems. This section provides an overview of the Public Transport program, listing the program’s primary capabilities, required inputs and generated outputs, and discussing how you can use the program to prepare data and model public transport systems. This section also discusses terminology used within this document.

Topics include:

• Summary of facts

• Preparing data

• Modeling

• Heuristic Process

• Terminology

Summary of facts

The Public Transport program offers:

• User control over all aspects of the Public Transport model

• True multirouting between zone pairs, or alternatively single best-path routes may be used

• Demand stratification by user class with variations in the behavior of classes represented by different cost functions

• Comprehensive fares modeling

• Preparation of a public transport network for Public Transport’s modeling functionality

• Generation of the nontransit element of the public transport network (that is, access, egress, transfer and park and ride legs)

• Skimming, network-wide and mode specific, composite and average travel costs, and components of costs

• Two methods (service-frequency and service-frequency-and- cost) for loading demand on to transit choices at stops

• Analyses of loaded trips—transfers between modes, operators, lines, a variety of stop-to-stop movements, select-link/line outputs

• Reporting of input data, model infrastructure, multiple routes with probability of use, line and link loads, secondary analyses

The Public Transport program requires as input:

• A highway or public transport network

• Public transport system data

• Line data

• Fare data

• Nontransit legs (developed externally or by Public Transport)

• Generalized cost information

• Demand

The Public Transport program produces:

• Nontransit legs

• Enumerated routes

• Skim and select-link matrices

• Loaded lines and nontransit legs

• Transfer matrices—results of loading analyses

• A variety of reports of input data and model results

• A public transport network that can be displayed by CUBE and used as an input network for further modeling

Preparing data

You can use the Public Transport program to prepare data that supports public transport modeling. You can prepare:

• A network, produced by Network or Public Transport, containing characteristics of zones, nodes and links (that is, node coordinates, walk and transit link times, distance, and so forth), over which the public transport system operates.

• System information used to describe the characteristics of the public transport system such as modes, operators and wait curves.

• Service or line data, defining the characteristics of the lines and nodes traversed.

• Nontransit legs, presenting opportunities to access the public transport system, egress from it and transfer between services during the course of a trip. Nontransit legs may be determined externally and/or generated by Public Transport under user control.

• Control information for route enumeration and evaluation.

Modeling

You can use the Public Transport program to model public transport. The model has several parts:

• Route enumeration and evaluation

• Skimming (levels of service matrices)

• Loading (assignment)

• Reporting

Route enumeration and evaluation

During route enumeration and evaluation, the Public Transport model finds "reasonable" or "attractive" multiple discrete routes between zones, considering:

• Number of transfers

• Spread — the margin of cost over the minimum cost route

• Nontransit and in-vehicle costs

• Boarding and transfer penalties by mode

• Waiting time, derived from the combined frequency of services at stop nodes

• Fares (considered only for evaluation)

Skimming (levels of service matrices)

During skimming, the Public Transport model skims (extracts) the costs—and the components of costs—of journeys between zones. These costs are suitable for model validation, demand modeling, scheme evaluation, loading demand on the network and producing operational statistics like passenger miles, hours and revenue. The model can extract the following skims:

• Composite costs

• Value of choice

• Average, perceived, and actual trip costs and components (that is, nontransit, in-vehicle and wait times, boarding and transfer penalties, fares)

• Best trip cost

The model can extract network-wide trip costs, or the model can stratify them, where appropriate, by modes.

Loading (assignment)

During loading, the Public Transport model loads demand, in the form of trips between zone pairs. The model uses a series of models at the different decision points in a trip:

• The walk-choice model allocates trips between attractive choices at access, egress, and transfer points. Where walk and transit choices are available, it also determines the transit share.

• The service-frequency or the service-frequency-and-cost model allocates the transit share at a stop between the attractive services available at that stop.

• The alternative-alighting model apportions the share of a service to the attractive alternative alighting points of that service.

(Strictly, these models determine the probability of use of the alternative routes; trips are then loaded on the routes based upon these probabilities.)

Two forms of loading are supported, multirouting and best-path. The best-path method does not use walk or alighting choice models, and loads demand using the service-frequency model.

Reporting

During reporting, the Public Transport model produces reports you can use to analyze different aspects of passenger loadings:

• Passenger transfers between all modes

• Passenger transfers between public transport modes

• Passenger transfers between operators

• A variety of stop-to-stop movements

Heuristic Process

The Public Transport modeling algorithm implements a sequence of rules (network simplification > minimum path > enumeration > evaluation (decision points probabilistic models > combination of probabilities at the different decision points) / iterative route evaluation step in case of crowding) to find an "approximate/feasible solution" close to the optimal solution. This approach can be defined an heuristic process.

It is therefore important that once the model is defined in terms of the system, lines and parameters, this fundamental structure of the Public Transport model is kept consistent with the analysis that needs to be undertaken in different scenarios. The results from the model could be sensitive to major changes in the inputs due to the heuristics in network simplification, route enumeration and evaluation.

This consistency between the base scenarios and the forecasting scenarios is a general rule that should be followed, referring to the attributes coded to describe the Public Transport model (modes numbering system, etc.). In particular, the line ordering should be defined in the base scenario, and the model should be calibrated accordingly. This line ordering, consolidated in the base scenario, should be kept consistent in forecasting scenarios, whilst new lines should be added at the end of the line file or in a new line file.

Terminology

This document uses the following sets of terms interchangeably:

• "transit" and "public transport". In particular, "transit" is used in this document to describe a type of link over which a public transport service can run, namely "transit link" as opposed to "nontransit link".

• "lines" and "services"

• "transfers" and "interchanges"

• "skims" and "levels of service"

• "generalized cost" and "generalized time"

• "origin-destination pairs", "zone pairs", "OD pairs", and "IJ pairs"

• "nontransit time" and "walk time"

• "loading" and "assignment"

• "volume", "load", "flow", and "passenger flow"