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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

Transit Path Building

Transportation leadership you can trust.

presented toFlorida Transit Modeling Workshop

presented byThomas RossiCambridge Systematics, Inc.

April 8, 2004

objectives in transit path building
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
path building options in transcad
Path Building Options in TransCAD
  • Shortest path (all-or-nothing)
  • Optimal strategies
  • Pathfinder
  • User equilibrium (assignment)
  • Stochastic user equilibrium (assignment)
impedance in path choice
Impedance in Path Choice

Egress time

Dwell time

Number of transfers


  • 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

non transit links
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
time of day
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


    • Between mode choice and assignment
path choice example
Path Choice Example

Rail – 30 min headway, 30 min travel time



Bus – 20 min headway, 45 min travel time

ensuring that paths use the chosen mode
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
use of weights
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
other considerations
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