Travel demand modeling is a computer-based tool that is used by the NJTPA to help with analyzing projects, developing the long range plan, and determining compliance with air quality conformity standards. The NJTPA has enhanced the travel demand model used in the region and a preliminary version is beginning to be applied. Below are brief descriptions of both the current travel demand model and the newly enhanced model.
The North Jersey Regional Transportation Model (NJRTM)
The model historically used by the NJTPA is called the North Jersey Regional Transportation Model (NJRTM). The NJRTM is a standard four-step transportation model built with TRANPLAN software. The standard four steps are:
- trip generation, where the number of trip origins and destinations are estimated;
- trip distribution, where trip origins are matched with trip destinations;
- mode choice, where a travel mode (e.g., single occupant vehicle, transit) is assigned to each trip; and
- trip assignment, where the route that each trip takes from origin to destination is estimated.
The area analyzed by the model consists of the thirteen county North Jersey region; external stations are used to represent travel to and from places outside the region (such as New York City). The model was largely developed in the late 1980s by the New Jersey Department of Transportation (NJDOT) and has been subsequently enhanced by the NJTPA and NJDOT in various stages. The NJRTM is also used by NJDOT for a variety of applications, including as an element of a larger New Jersey statewide travel model.
Characteristics of the NJRTM model
The NJRTM model has 1,377 traffic analysis zones and 74 external stations. The highway network includes most arterials (major and minor) including most 500 level county roads but does not include many collector or local roads. There are three separate networks for the three different time periods used for running the model: AM peak (6:30am to 8:30am), PM peak (3:30pm to 6:00pm) and off peak (all other times).
The model has four trip purposes:
- Home Based Work (trips between home and work),
- Home Based Shopping (trips between home and shopping destinations),
- Home Based Other (all other trips from or to home), and
- Non-Home Based (all other trips that has home as neither an origin nor destination, e.g., a trip from work to the movies).
The model has six modes for most trip purposes (seven modes for the Home Based Work trip purpose):
- trucks,
- driving alone (SOV),
- carpooling with 2, 3, or more occupants per vehicle (HOV-2, HOV-3, HOV-4+ (only for Home Based Work)),
- walking to transit, and
- driving to transit.
The model also includes a unique accessibility feedback loop that reallocates a small amount of forecasted demographic growth based on a measure of accessibility for each zone after the first model assignment iteration.
The North Jersey Regional Transportation Model - Enhanced (NJRTME)
The NJRTM is not the only model currently used in the region. New Jersey Transit created a separate model (the New Jersey Transit Demand Forecasting Model or NJTDFM) to more accurately model transit demand in the region. This model does not encompass a full four-step process; it bypasses trip generation and builds distribution patterns from a synthetic trip table based on travel surveys. The specialized nature of the NJTDFM makes this model unacceptable for MPO air quality conformity testing purposes.
There was a realization among the transportation agencies in North Jersey that improvements were needed in the travel demand forecasting tools currently being used. Therefore, the North Jersey Regional Transportation Model - Enhanced (NJRTME) project began as an effort to produce a fully functioning transportation forecasting tool that is comprehensive and powerful enough to fulfill the regional modeling needs of all major transportation agencies in the region.
Characteristics of the NJRTME model
Platform: The enhanced model remains a standard four-step model, now running on a Citilabs software platform (CUBE interface, Voyager and TP+) with additional FORTRAN programs used within mode choice estimation.
Zonal System: The NJRTME has 2,545 traffic analysis zones (about 1,800 of these are in the NJTPA region) and no external stations. The model has been expanded to include all of New York City and Long Island, and portions of southern New Jersey, southern New York State, and eastern Pennsylvania.
Highway Network: Within the NJTPA region, the highway network includes most arterials (major and minor) including most 500 level and 600 level county roads but does not include some collector or local roads. Outside the NJTPA region, the highway network is more schematic, representing major regional roadways.
The model has eight trip purposes:
- Home-Based Work Direct (trips between home and work with no intermediate stops),
- Home-Based Work Strategic (trips between home and work with one or more intermediate stops),
- Home Based Shopping (trips between home and shopping destinations),
- Home Based Other (all other trips that either begin or end at home),
- Work Based Other (trips based at work, other than those associated with the trip from or to home),
- Non-Home-Non-Work (all other trips that have neither origins or destinations at home or work),
- Airport Trips (trips to or from regional airports), and
- University Trips (trips to or from regional colleges and universities made by students).
The model has six modes for most trip purposes (seven modes for the Home Based Work trip purpose):
- Trucks,
- SOV,
- HOV-2,
- HOV-3,
- HOV-4+ (only for Home Based Work),
- Transit-Walk Access, and
- Transit-Drive Access.
There is also a portion of the model that estimates non-motorized mode use (e.g., walking and biking).
The NJRTME retains the accessibility feedback loop from the original NJRTM to reallocate a portion of forecasted demographic growth according to the accessibility of each zone.
Transit Network: The transit network includes New Jersey Transit’s rail and bus system. The network also includes ferry services.
Trip Generation: The model uses population, household (with a split into households that contain retirees, households that do not contain retirees but contain children, and households with no retirees or kids) and income data.
Highway Assignment: There are four separate networks for the four different time periods in the model including expanded peak hour periods: AM Peak (6:00am-9:00am), Midday (9:00am-3:00pm), PM Peak (3:00pm-6:00pm), and Night (all other times).