Related Terms

acyclic subgraph

An acyclic subgraph is a network without cycles (a cycle is a complete circuit). When following the network from node to node, a node is never visited twice.

backward shortest path

A the shortest path computation that starts at the destination node. This is used when there is a preferred arrival time.

dynamic passenger assignment model

A model that simulates the performance (reliability) and dynamics (capacity constraints, interactions) of a system of passenger demand and scheduled or on-demand transportation services (transit, TNCs, taxis) that run on a physical transportation network.

dynamic transit passenger assignment model

A dynamic passenger assignment model that is designed for scheduled transit service.

forward shortest path

A shortest path computation that starts at the origin node. This is used when there is a preferred departure time.

hyperlink

A hyperlink consists of a set of transit links from a single origin to multiple possible destination nodes [ for forward-shortest-path finding ] or a set of links from a single destination to multiple possible origin nodes [ for backward-shortest-path finding ]. There may be multiple transit departures within a hyperlink.

hyperpath

An acyclic subnetwork with at least one link connecting the origin to the destination, and where at each node, there are probabilities for choosing the alternative links. In most hyperpath-based frameworks, this can be equivalent to the path choice set.

overlap scale parameter

The parameter in the path-size logit model that scales the impact of the path size term.

passenger simulation

Probabilistic assignment of passengers to paths in their pathset based on costs. Update of pathset feasibility.

path choice model

A mathematical model for selecting a path from a set of feasible choices. Examples include the recursive logit model, path-size logit model, Kirchhoff model.

path cost

Path cost or generalized cost is a measure of impedance on a network object. It is typically composed of different variables, each with a fixed weight. Terms may include cost, in-vehicle time, number of transfers, wait time etc.

path overlap variable

An additive measure of similarity between paths. In road-based path-choice models, this is often the distance of the shared links. In passenger-based path-choice models, this could include considerations for shared-routes, similar-routes, on/off stations, traversed stations, traverse distance and more. If the overlap variable is an indicator variable (𝛿), then it can be 1 or 0; if it distance or cost, then it is a continuous variable.

path overlap

In a set of possible paths through a transportation network, some portion of each of the paths may share a facility meaning that each choice in a choice set is not mutually exclusive. This is important in the context of choice modeling, since it violates the “Independence” in the IIA property of a Multinomial Logit. Formulations that compensate for this violation by discounting the “independence” of each path based on a measurement of commonality (the path overlap variable) include the path-size logit model.

path size logit model

A modified logit choice model where the utility equation for a path adds a path size variable to the utility of a path alternative in order to account for overlap between different path options.

path weight parameters

Coefficients on various components of the utility equation for the path choice model. Can be estimated, asserted, or inferred. Path weight parameters can either be based on a link feature (i.e. in-vehicle time) or path feature (i.e. directness). The path weight parameters can vary by user class.

pathfinding probability

The probability of each path in the pathset based on the pathfinding cost. Differs from simulated probability in that the simulation step hasn’t occurred yet so the probabilities are subject to change; for example, some paths may become infeasible if the simulation fills up some vehicles so the the passenger cannot board the vehicle for this leg. May also include path overlap penalties (although Fast-Trips doesn’t calculate it in Pathfinding, only in Simulation).

joint person tour

A set of paths between an origin and destination with specific costs, waypoints, and timings. In hyperpath-based frameworks this is often derived from the hyperpath.

predicted passenger path choice set links

A list of links for a predicted path set/hyperpath, with their timing and costs, that the passenger considers taking.

predicted passenger path choice set

A list of feasible paths, with their timing and costs, that the passenger considers taking for a specific trip. In some frameworks, hyperpaths can be used to create the path choice set.

stop label

In the context of a shortest path algorithm, stops are labeled with the overall generalized cost of travelling from that stop to the destination (in a forward shortest-path) or from that stop to the origin (in a backwards shortest-path). Stops can be iteratively updated throughout the algorithm.

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