.. module:: wsa.TNC

.. toctree::
   :maxdepth: 2
   :caption: Contents:


Step 7 - TNC Trips
============================
This script estimates the number of TNC trips by TAZ based on a trip table,
modal skims (to understand costs by the estimated mode and estimate costs
for a potential TNC trip), and *alpha* values. The probability for taking a
TNC trip given its generalized cost must exceed the probability of taking the
same trip by the original estimated mode by a factor that exceeds the alpha
value set for that mode and travel purpose.

This is a post-processing step that ingests ouptuts from previous steps to
provide insight into the number of TNC trips made and what those trips
imply for mode shifts.

TNC trip cost parameters are specified as global parameters: `TNC_BASE_FARE`,
`TNC_SERVICE_FEE`, `TNC_COST_PER_MILE`.

Alpha values may be calculated when the script is run to calibrate them to
targets for aggregate TNC trips by purpose and mode replaced. Once calibrated
to a base condition, the same values should be run for alternative scenarios
or alternative TNC cost constructions to gauge the impact on TNC utilization.

The script summarizes TNC estimates in two csv tables:

- **TNC_flow_summary_{period}.csv**: csv
    Reports TNC trips by purpose and mode replaced for generalized reporting
    geographies (focus, window, and remainder areas). Summarizes TNC trips,
    total trips (in the original trip tables), and percent switchted to TNC.

- **TNC_zone_summary_{period}.csv**: csv
    Similar to `TNC_flow_summary`, but broken down on a TAZ-by-TAZ basis.

Functions
----------
The following functions are referenced in this script, from the 
`wsa.TNC` submodule:


.. autofunction:: fetchTNCSeed

.. autofunction:: fetchTNCModeTargets

.. autofunction:: estimateAlphas

.. autofunction:: initTNCCostArray

.. autofunction:: initTNCRatioArray

.. autofunction:: estimateTNCCosts

.. autofunction:: estimateTNCProb

.. autofunction:: applyTNCProbRatio


* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`