Reports & Facts

Reports

Overview

Printable Triangle Regional Model (TRM) Overview (pdf opens in a new window, 53 kb)

Summary of Triangle Region

The Triangle Region includes the Capital Area Metropolitan Planning Organization (CAMPO) and the Durham-Chapel Hill-Carrboro (DCHC) Metropolitan Planning Organization (MPO) in addition to portions of several collar counties including Chatham, Harnett, Johnston, Franklin, and Granville Counties. The total estimated population for this region in 2002 was 1,149,114 persons. In addition to being home to Research Triangle Park, the Triangle region is also home to two major medical centers, one housed at Duke University in Durham and the other housed at the University of North Carolina, Chapel Hill. Duke University and the Medical Center is the largest single employer in the Triangle region. Raleigh is the largest municipality in the region, originally developed as a government center around the state capital in the downtown. Raleigh is also the location for North Carolina State University.

In addition to the municipalities of Raleigh, Durham, and Chapel Hill, the region consists of other cities and towns that impact travel decisions in the Triangle. Chief among these is Cary with approximately 108,000 residents in July of 2004. The many jobs in this region draw commuters from rural areas and communities for many miles, and this represents a major challenge for the travel model. Regional demographics are provided in Table 1 below.

*Source: 2000 Decennial Census

Organizational Structure for Modeling in the Triangle Region

The Triangle Regional Model (TRM) service bureau, in cooperation with regional stakeholders (CAMPO, DCHC-MPO, NC Department of Transportation, and the Triangle Transit), performs the travel modeling for the region. The service bureau is a diverse team of professionals with backgrounds in planning, engineering, travel modeling, and environmental analysis housed at NC State University, Institute for Transportation Research and Education. The primary objective of the TRM service bureau is to develop, maintain, update, and conduct training related to the Triangle model. A secondary objective is to facilitate and conduct research related to travel modeling and transportation planning.

Characteristics of the Model

• The modeled area covers approximately 2,600 square miles divided into 2,317 internal Traffic Analysis Zones and seventy two external stations.
• The current base year for the model is 2005.
• The model operates on the TransCAD software platform.
• The roadway network has approximately 15,500 links stratified by urban, suburban and rural area types, and by federal functional classification system.  Zones are connected to the roadway network by 4,300 centroid connectors.
• The model network contains transit routes for six transit service providers: Capital Area Transit (CAT), NC State University Wolfline, Triangle Transit, Durham Area Transit Authority (DATA), Duke University Transit, and Chapel Hill Transit (CHT).  There are 179 peak routes and 138 off peak routes.

Current Structure of the Triangle Regional Model

Model Inputs

• Population
• Households
• University Dormitory Residents and Off Campus Students
• Mean Income
• Employment by Category (Industry, Retail, Special Retail, Office, Service)
• Special Generators (regional shopping malls, regional hospitals, universities, Raleigh-Durham International Airport)

Trip Purposes

• Home-based Work
• Home-based K-12 School
• Home-based Shopping
• Home-based Other
• Non Home-based
• Home-based University Student
• Internal Commercial Vehicles
• Internal/External Commercial Vehicles
• Internal/External Passenger Autos
• Through Passenger Autos
• Through Commercial Vehicles

Trip Generation

• Productions based on trip frequency share model stratified by five household categories (zero car households, low income households with cars, medium income households with cars less than workers, medium income households with cars equal to or greater than works, and high income households with cars).
• Attractions based on share model for the same five household categories.

Trip Distribution

• Destination choice model
• Separate peak and off-peak time periods
• Stratified by five household categories

Mode Choice

• Nested logit model
• Top level of the nest is auto and transit
• Lower level of the transit nest is local, express and rail services
• Lower level of the auto nest is drive alone, shared-ride 2, and shared-ride 3+
• Lowest level of the transit nest is stratified by access modes: walk, park & ride, and kiss & ride (drop off)

Highway Assignment

• AM Peak 4-hours (6:00 a.m. – 10:00 a.m.)
• PM Peak 4-hours (3:30 p.m. – 7:30 p.m.)
• Off Peak 16 hours
• User Equilibrium with maximum 99 iterations
• Conical volume delay function

Model Feedback

• Congested times are fed back to trip distribution and are iterated until convergence of the whole model is achieved.