TRANSIMS

How TRANSIMS Compares to 4-Step Models

	Different From 4-Step Models	Similar to 4-Step Models
Framework	The microsimulation and travel behavior sub models in TRANSIMS share data easily. Model iteration works with individual travelers rather than aggregate demand data. Time is a continuous variable throughout the framework.	TRANSIMS provides a collection of software modules and utilities to build models of travel demand and transport networks.
Travel demand generation	TRANSIMS models and tracks travel for each individual and vehicle. The TRANSIMS activity model uses a statistical sampling method to draw an activity pattern for a modeled household from a demographically similar survey household.	TRANSIMS may estimate demand from a zonal rate-based model.
Destination choice	Destination choice for each trip is made for each traveler rather than aggregate trips by purpose by zone.	Zonal interchanges can be estimated with a user defined gravity model. Choice of intermediate destinations on a tour may also be estimated.
Mode choice	TRANSIMS applies a user defined mode preference for each traveler. All travel starts and ends with a walk segment and transfers are explicitly routed as walks. For a given trip, the TRANSIMS Router may find that walking is a better choice than a vehicle and use walk for that particular trip.	Modes are user defined. The mode preference model structure is user defined. Applications to date use zone-zone auto and transit impedance with terminal characteristics as preference variables. The Router makes the final walk vs. vehicle choice. Walking, bicycling, SOV, auto passenger, transit bus, school bus, fixed guideway transit, and park-and-ride have been modeled to date.
Route choice and simulation	TRANSIMS uses a routing network representing all available transport services with facility service quality aggregated to fifteen-minute intervals. Path finding is link based. The Router relies on the Microsimulator to provide expected link travel times. The Microsimulator is an integral part of the TRANSIMS tool set.	TRANSIMS finds the shortest time path between two points on a network. Cost variables can be incorporated using a value of time for each traveler. All-or-nothing, iterative capacity-restrained, and (Nash) equilibrium assignment methods can be replicated.

	Different From 4-Step Models	Similar to 4-Step Models
Time	Traveler itineraries and subsequent vehicle uses are scheduled according to a travel survey and refined based on simulation results. Demand is estimated to the minute and simulated to the second.	Trip time of departure can be estimated using diurnal factors. Results can be aggregated to the hour, period or entire day.
Data	Networks Stop signs, traffic signalization, and intersection lane geometries need to be coded. Land Use, Population and Employment data TRANSIMS generates trip-end locations automatically, they must be refined manually. Monitoring and Surveys In addition to other data TRANSIMS reads 15-minute ATR/ATC/ITS data.	Networks A link-node format is used to describe topology. Existing network data or a commercial GIS dataset can provide the basis for an initial highway network. Existing headway and route data may be used to generate initial transit files, schedules and run details. The network database needs to be appropriately corrected and calibrated. Land Use, Population and Employment data Existing zone and parcel data may be allocated to activity locations. Census data, including SF3 and PUMS data are key elements for population synthesis, augmented by demographic forecasts for future years. Monitoring and Surveys Household activity survey External stations counts, forecast, intercept survey Transit on-board surveys Traffic count databases
Computing Environment	A Linux server or Linux cluster is used for model application. The framework is scalable to allow more computers to be used on larger, more complex problems.	Model results are analyzed using Windows or Unix workstations.

Different From 4-Step Models

Similar to 4-Step Models

Time

Traveler itineraries and subsequent vehicle uses are scheduled according to a travel survey and refined based on simulation results. Demand is estimated to the minute and simulated to the second.

Trip time of departure can be estimated using diurnal factors. Results can be aggregated to the hour, period or entire day.

Data

Networks
Stop signs, traffic signalization, and intersection lane geometries need to be coded.

Land Use, Population and Employment data
TRANSIMS generates trip-end locations automatically, they must be refined manually.

Monitoring and Surveys
In addition to other data TRANSIMS reads 15-minute ATR/ATC/ITS data.

Networks
A link-node format is used to describe topology. Existing network data or a commercial GIS dataset can provide the basis for an initial highway network. Existing headway and route data may be used to generate initial transit files, schedules and run details. The network database needs to be appropriately corrected and calibrated.

Land Use, Population and Employment data
Existing zone and parcel data may be allocated to activity locations. Census data, including SF3 and PUMS data are key elements for population synthesis, augmented by demographic forecasts for future years.

Monitoring and Surveys
Household activity survey
External stations counts, forecast, intercept survey
Transit on-board surveys
Traffic count databases

Computing Environment

A Linux server or Linux cluster is used for model application. The framework is scalable to allow more computers to be used on larger, more complex problems.

Model results are analyzed using Windows or Unix workstations.