ShadowPrice

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The mandatory destination choice models limit the number of workers (or students) who work (or attend school) in a given location via shadow pricing. For example, consider a travel analysis zone, label it X, in which 50 people work (i.e. the zone's employment is 50). In the first pass of the destination choice model, 200 workers choose zone X has their workplace location. Because zone X is oversubscribed, an additional disutility (or shadow price) is applied to zone X and the destination choice model is executed again. This process continues, per the user's preference, with a goal of limiting the number of workers who work in each zone to the employment of each zone. Mechanically, the "size" terms for each destination are scaled by the total origins to determine the maximum number of travelers allowed in each sub-zone.

The table below defines each of the columns in the shadow pricing output files. Note that the below columns are written for the following trip purposes (substitute these names for <purpose>): work_low, work_med, work_high, work_very_high, university, school_high, school_grade.

Name	Definition
alt	A unique identifier of the alternative considered in the destination choice model. The alternative is a unique zone/sub-zone combination.
zone	The travel analysis zone of the alternative
sub-zone	The walk-to-transit destination sub-zone
<purpose>_origins	Tours generated at this zone/sub-zone
<purpose>_sizeOriginal	Size term, which is specified in the UtilityExpressionCalculator, for each destination alternative
<purpose>_sizeAdjOriginal	Shadow pricing routine allows the user to intervene by manually adjusting size terms -- not implemented in our travel model
<purpose>_sizeScaled	Size term scaled ...
<purpose>_sizePrevious	Size term from the previous iteration of shadow pricing
<purpose>_modeledDests	Number of simulated destinations for each alternative (sum should equal sum of origins)
<purpose>_sizeFinal	Size term to be used for the next iteration of shadow pricing
<purpose>_shadowPrices	Shadow price for the alternative, which is !sizePrevious divided by !modeledDests

-- Main.DavidOry - 25 Jul 2012