Transcript CS Standard PowerPoint Template

Transit Path Building
presented to
Florida Transit Modeling Workshop
presented by
Thomas Rossi
Cambridge Systematics, Inc.
April 8, 2004
Transportation leadership you can trust.
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
Shortest path (all-or-nothing)
Optimal strategies
Pathfinder
User equilibrium (assignment)
Stochastic user equilibrium (assignment)
Impedance in Path Choice
In-vehicle time
Egress time
Initial wait time
Dwell time
Transfer wait time
Number of transfers
Access time
Costs
To ensure consistency with mode choice, variables
used and their weights should be consistent with
mode choice utilities
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
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
Path Choice Example
Rail – 30 min headway,
30 min travel time
Origin
Destination
Bus – 20 min headway,
45 min travel time
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
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
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