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Transit Path Building

Transit Path Building. Transportation leadership you can trust. presented to Florida Transit Modeling Workshop presented by Thomas Rossi Cambridge Systematics, Inc. April 8, 2004. Objectives in Transit Path Building. Development of skims for mode choice (and maybe trip distribution)

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Transit Path Building

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  1. Transit Path Building Transportation leadership you can trust. presented toFlorida Transit Modeling Workshop presented byThomas RossiCambridge Systematics, Inc. April 8, 2004

  2. Objectives in Transit Path Building • Development of skims for mode choice (and maybe trip distribution) • Transit assignment • Need for consistency in path building throughout the modeling process

  3. Path Building Options in TransCAD • Shortest path (all-or-nothing) • Optimal strategies • Pathfinder • User equilibrium (assignment) • Stochastic user equilibrium (assignment)

  4. Impedance in Path Choice Egress time Dwell time Number of transfers Costs • In-vehicle time • Initial wait time • Transfer wait time • Access time To ensure consistency with mode choice, variables used and their weights should be consistent with mode choice utilities

  5. Non-Transit Links • For walk access/egress paths, include street layer—NOT necessarily the same as highway network—and centroid connectors • For auto access paths, include highway network and centroid connectors

  6. Time of Day • To ensure consistency, mode choice and transit assignment must be performed for the same time periods, for example: • Between trip distribution and mode choice • Between trip generation and distribution BUT NOT • Between mode choice and assignment

  7. Path Choice Example Rail – 30 min headway, 30 min travel time Origin Destination Bus – 20 min headway, 45 min travel time

  8. Ensuring that Paths Use the Chosen Mode • Affected by how alternatives are defined: • Rail only • Bus only • Bus and rail • Access modes • Use of selection sets • Use of weights on links by mode • Weights may be inconsistent with mode choice utilities • However, may need weights to ensure consistency

  9. Use of Weights • Increasing the probability of using the chosen mode • Example: For a rail path, multiply rail time by 0.75 (keep bus time weight at 1.00) • Minimize the possibility of having paths with mostly (or all) non-transit links • Example: Increase non-transit link weight to > 1.0 • Use the chosen access mode • For transit-auto access paths, increase weight for walk access links

  10. Other Considerations • No set limits on variables • Wait times • Walk access times • Walk egress times • Auto access times • Transfer times/distances • Number of transfers • Alternatives • Non-linear functions • Piecewise linear functions

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