Transportation leadership you can trust. presented to Florida Transit Modeling Workshop presented by Thomas Rossi Cambridge Systematics, Inc. April 8, 2004 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 Shortest path (all-or-nothing) Optimal strategies Pathfinder User equilibrium (assignment) Stochastic user equilibrium (assignment)

Impedance in Path Choice In-vehicle time Initial wait time Transfer wait time Access time Egress time Dwell time Number of transfers 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 Bus – 20 min headway, 45 min travel time Origin Destination

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