Mode Choice#
The mode choice model in POLARIS is a nested logit model. It incorporates nine modes, including walking, biking, car-driver (named SOV), car-passenger (named HOV), taxis, transit, park-and-ride, park-and-rail, and TNC-and-ride. The root of the mode choice model includes walking, park-and-ride + bike nest, auto nest, rail nest, transit, and TNC-and-ride modes. SOV, HOV, and taxis are nested under the auto mode; the rail nest includes rail transit and park-and-rail modes, and finally, the park-and-ride mode and biking make up the park-and-ride + bike nest.
Additional availability checks are incorporated based on various conditions, such as household vehicle availability and walking distance to transit stations, as well as scenario settings. Each mode has its utility calculated separately, which includes trip properties, land-use characteristics, and demographic information of the trip-makers. The value of travel time (VOTT) is calculated for each trip-maker based on the base mode and activity type, and the VOTT is further adjusted based on the particular mode specified in the mode choice model. Travel times and distances are extracted from the skims for each mode. Travel costs are further processed based on in-vehicle and out-vehicle times, based on different access and egress mode if that applies. Demographic information includes gender, age, education, vehicle ownership, household income, and other factors.
Derived Modes#
Some mode types like the combination of available modes (especially first-mile-last-mile) type of trips are difficult to estimate from survey data owing to small shares. In such cases, mode preferences are derived from the combination of preferences and this new choice option is added such that it does not conflict with the remaining choice set. First-mile-last-mile choice utilities are calculated during mode choice by incorporating different existing estimates, including:
FMLM part that includes the alternative specific constants, travel cost of TNCs and rail.
demographic parameters and variables that are calibrated for the transit modes
demographic parameters and variables that are calibrated for taxi modes.