Simpson County Travel Demand Model

July 22, 2003

BACKGROUND

•WSA started working on KY 1008 Pre-Design Scoping Study in November 2002

•Currently, there is ¾ of a Bypass (KY 1008) around Franklin, Kentucky

•Planning project aimed to determine need (if any) for full bypass

•Traffic would be important in justification of new segment

•As a result, the KYTC made the decision to develop travel demand model to coincide with study

BACKGROUND (CONT.)

•Project coordinated through the Divisions of Planning and Multimodal Programs

•KYTC decided to build full travel demand model for Simpson County for future uses

• Air quality analysis (non-attainment)

• Other transportation improvements

BACKGROUND (CONT.)

STUDY AREA

• Roadway Coverage / Network

• Traffic Analysis Zones

• Model Development

• Trip Generation

• Trip Distribution

• Traffic Assignment

MODEL DEVELOPMENT

ROADWAY COVERAGE

• Roadway Coverage includes:

• All state-maintained roads in Simpson County

• I-65 (North / South)

• US 31W (North / South)

• KY 100 (West / East)

• Many local roads

• County Roads

• City Streets

ROADWAY COVERAGE

TRAFFIC ANALYSIS ZONES

• Traffic Analysis Zones were based upon:

• Census Blocks / Census TAZs

• The highway network

• Socioeconomic Data included:

• Census Bureau

• Dun & Bradstreet Employment Data

• Franklin-Simpson Industrial Board

• KYTC District 3

3-STEP MODEL

• Automated using GISDK User Interface

• Trip Generation (Quick Response Method)

• Trip Distribution (Gravity Model with Gamma Function)

• Traffic Assignment (User Equilibrium)

GISDK USER INTERFACE

• Originally developed for the Madisonville UATS

• Easily moved from model to model

• Simplified each model run

• Included Error-Prevention Strategies

RESULTS

•Very good initial runs

•Particular consideration given to calibration in Franklin and areas near bypass

•Met FHWA calibration requirements

• Overall RMSE < 30%

• RMSE requirements achieved for all functional classifications

• Also, met RMSE requirements for volume groups

FRANKLIN BYPASS EXTENSION

•The calibrated base year model was used to forecast traffic patterns for the Future Year 2025

•As mentioned, the number of vehicles expected to utilize new bypass extension was very important

•Result ranged from 6,500 – 7,000 vehicles per day on the bypass (Year 2025)

TRUCK COMPONENT

•E-E truck trips are a major source of truck trips in the study area along major north/south routes (I-65/US 31W)•External-External (E-E) truck trips were simulated for this project based on existing truck counts

• Internal truck trips is currently being developed

BPR CURVE

•Speed Estimation has been important topic recently for the KYTC

•KYTC asked to use updated BPR function parameters:

• a = 0.05 (signalized); 0.2 (other)

• b = 10

•Currently, conducting sensitivity analyses to study the difference between default BPR (a=0.15; b=4) parameters and updated BPR parameters

MOBILITY ANALYSIS

•Another important topic for KYTC is Mobility Analysis

•Currently, researching TTI methodology for computing congestion using:

• Travel Time Index

• Travel Rate Index

•Result will be an overall value (or index) for quantifying congestions for an urban area (or other specified area)

Questions?