cost.functions: Construct cost functions
In travelr: Functions for Travel Demand Modeling

Description Details Value Author(s) See Also

Cost functions (Volume/Delay) are used to establish equlibribum conditions for highway assignment.

Cost functions are called from within the assignment algorithms (highway.assign like this:

1	cost.function(volume,aset)

The parameters have the following definitions:

volume: volumes for which costs are to be computed; see below
aset: An assignment.set describing the classes in the assignment

The function returns a data.frame with one column per assignment class, each of which contains the numeric routing cost for the network links for vehicles in that class. (The routing cost is the network link value that will be minimized when building shortest paths for assigning vehicles of the class).

The assignment set is passed to the function so that different assignment classes in the set may have their costs evaluated separately. That can be useful if, for example, certain assignment classes have routing costs that are evaluated differently than other classes. Passenger vehicles, for example, may be considerably more sensitive to the presence of other trucks.

If the assignment set is defined with a cost.volume.type of “vector”, the volume passed to the cost function will be a vector corresponding to the sum of all the class volumes on each link. Otherwise, if the cost.volume.type is “matrix”, a data.frame will be passed with the link volume for each class in its own column.

Helper functions are available to construct cost (and objective) functions in the classic form known as BPR (Bureau of Public Roads).

cost.function returns a numeric vector or data.frame of the same shape as volume

Jeremy Raw

assignment.set for a description of how the cost function is used. bpr.functions for BPR helper functions http://emme2.spiess.ch/conic/conic.html for a technical discussion of some alternative cost functions

travelr documentation built on May 2, 2019, 5:17 p.m.