Trip Generation Discussion

1
Trip Generation Discussion
Kentucky Model Users Group Meeting
May 27, 2004
2
Topics

• Recent Projects
• Trip Purposes
• Variables
• Trip Rates
• External Trips

3
Recent TDMs

• County Level Models
• Simpson County (KY)
• One Uniform Trip Rate
• Hopkins County (KY)
• One Trip Rate Used
• Multiple Trip Rates Tested (Rural / Urban)
• MPO
• Radcliff / Elizabethtown, KY (Hardin / Meade
  Counties)
• Tested Rural / Urban and Income Level

4
Trip Purposes

• Typical WSA model (in Kentucky) will include
• Home-Based Work (HBW )
• Home-Based Non-Work (HBNW)
• Non-Home Based (NHB)

5
Trip Purposes (cont.)

• Other trip purposes do exist
• School / College
• HBW versus HBW-related
• The usage of different purposes often depends on
• Size of study area
• Available data (surveys, etc.)
• Budget

6
Advantage / Disadvantages

• HBW, HBNW, and NHB trip purposes seem to work
  well on the models WSA develops in Kentucky
• Advantages
• Traditionally good results
• Not overly complicated
• Allows some flexibility during calibration
• Disadvantages
• Not detailed enough to fully represent all
  characteristics of modeled area
• Often based on general data (national sources,
  etc.)

7
Dependent Variables

• Productions
• Typically based on households
• Primary source is the United States Census Bureau
• Attractions
• Typically based on employment
• Retail
• Non-retail
• Sources include state databases and Dun
  Bradstreet (DB)
• State databases are good for control totals
• DB is good for employment concentrations
• DB breaks data into classifications

8
Trip Generation Procedures

• Quick Response Method (QRM) older approach
• Relies upon NCHRP 187 rates
• Typically, these rates were modified during
  calibration
• Recent approach
• Similar to QRM, but table is less complicated
• Use trip purposes and other factor
• Income
• Rural / Urban
• Ties into user interface
• Initial rates based on NCHRP 365 values

9
Trip Rate Sources

• NCHRP 187
• NCHRP 365
• National Household Travel Survey (NHTS)
• Surveys (if available)
• Rates are adjusted during calibration since the
  rates above are general rates

10
Deviation of Trip Rates

• Recent Trip Rate Usage
• Uniform trip rate
• Urban vs Rural
• Income
• Other Variables

11
Special Generators

• Radcliff / Elizabethtown MPO TDM
• Fort Knox is a major component in this model
• Due to increased security, travel into Fort Knox
  occurs at three gates
• Fort Knox provided us with traffic volumes in and
  out
• Added as special generator, but treated similar
  to external station

12
External Trips

• Step 1 Determine external routes and functional
  classification of those routes
• Step 2 Make sure the traffic counts are current
  on external routes
• Step 3 Determine difference between
  External-External and External-Internal
• Functional Classification
• KYSTM
• Equations
• Local Knowledge

13
Model Calculations

• Internal or External to TransCAD?
• WSA prefers to perform Trip Generation within
  TransCAD
• Why?
• Less complications of importing / exporting files
• Can easily be repeated
• Is easily incorporated into user interface

14
Lessons Learned / Next Steps

• Smaller models do not require as much deviation
  of trip rates
• Sophistication of trip generation techniques
  increase as complexity of modeled area increases
• More time needed to continue to explore other
  trip generation procedures, rates, etc.