KY MUG Network and Trip Generation Issues

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KY MUGNetwork and Trip Generation Issues

• The Corradino Group
• May 27, 2004

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Some Network Issues

• Base Map and Projection
• All roads or just model network roads?
• One big file or a new file for each alternative?
• Calculation of speeds and feedback
• Calculation of capacities
• Other attributes
• Node attributes and turns
• Storage of results

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Some Trip Generation Issues

• Type of Model
• Traditional trips
• Activity-based or trip chains
• Number and definitions of trip purposes
• Special considerations, e.g., universities, state
  government, tourism
• Availability of data zonal data and surveys
• Productions cross-class (need a household
  model),
• Attractions trip rates
• Special Generators
• Implementation Spreadsheet, model script

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Networks Base Map and Projection

• Somewhat dependent on software. TransCAD works
  well with lat/lon.
• Best to use true shapes with GIS distances, not
  stick maps.
• If state plane, most agencies use NAD83 datum.
• Tiger, commercial sources like GDT (licensing
  issues), some agencies have their own.
• Important to link with data that is regularly
  maintained, like HIS.

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Networks All roads or just model network roads?

• General recommendation use all roads and a
  selection set for modeled roads.
• Coding and testing alternatives
• Showing highway and transit access
• More realistic maps

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Networks A separate file for each alternative?

• Pros and Cons either way.
• One file makes comparisons easier.
• Backup even more important.
• Files become large.
• Most consistency issues eliminated.

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Networks Calculation of speeds and feedback

• Old way hard-coded speeds on each link not
  recommended.
• New way speed/capacity tables based on network
  attributes less arbitrary and subject to
  manipulation
• Better way speed calculator based on posted
  speeds and traffic control. Data?
• Feedback loops for consistent speeds recommended,
  but not yet prevalent. Can greatly increase the
  running time.
• Also look at the volume/delay function.

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Networks Calculation of capacities

• Much like speeds hard code, tables, calculators.
• Some agencies use capacity calculators.
• Most capacities controlled by intersections.
• Increased data requirements, but data are
  becoming more available.

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Networks Turn penalties and delays

• Turn penalties and prohibitors
• Static turn penalties
• Signal delays
• Dynamic assignment of penalties (TransCAD has
  some features)

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Networks Other link attributes

• Lanes, median
• Counts by TOD, direction, vehicle classification
• Area type, facility type, functional class
• K, D, T
• BPR alpha, beta (or other function)
• Jurisdiction
• In network?
• Others links with HIS (section, milepost)

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Networks Nodes

• More than coordinates
• Turns control
• Traffic control device information
• Type of node Centroid, intersection, external,
  etc.

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Networks Storage of results

• TransCAD puts the results in a separate database.
• Results can then be linked, moved or added.
• If results are added, an alternative management
  convention is needed.

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Trip Generation Type of Model

• Most areas used traditional trip models
• Some areas are implementing activity-based or
  trip chain models.
• Still experimental in terms of methods and
  software.
• Activity-based models are theoretically
  appealing, but require a time and budget
  commitment to research.

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Trip Generation Number and definitions of trip
purposes

• Why are multiple purposes needed?
• Pair up logical trip ends
• Different trip length distributions
• Simple structure
• HBW
• HBNW
• NHB
• External-External (EE)
• External-Internal (EI)

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Trip Generation Number and definitions of trip
purposes

• HBW
• HBNW
• School
• Shopping
• University
• Government
• Social/Recreational
• Other

• NHB
• Work related
• Not work
• External-External (EE)
• External-Internal (EI) Maybe part of internal
• Trucks Light-duty, Single Unit, Combinations

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Trip Generation Trends

• Consider intermediate stops to and from work.
• Careful consideration of unique local conditions
  more purposes
• Income or auto availability strata (for
  distribution)
• Combine EI with internal

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Trip Generation Availability of data

• Model governed by availability of independent
  variables.
• Home end US Census and special tabulations
  (Florida ST-60).
• Non-home end (employment) ES-202, commercial
  sources like InfoUSA, Dun Bradstreet.
• Special generators (special local conditions)

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Trip Generation Model Development

• National sources like NCHRP 365
• Borrow a similar area
• Small sample surveys (recommended)
• National Household Travel Survey
  http//www.bts.gov/programs/national_household_tra
  vel_survey/
• Census Transportation Planning Package

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Trip Generation Productions

• Rates for households classified by things like
  persons, workers, number or availability of
  autos, income (more prevalent), work status,
  presence of children.
• Need a household model to categorize households
  from aggregate numbers OR,
• Special Census tabulation as seed matrix.
• Linear regression seldom used.
• Avoid procedure with additive constants trips
  from empty zones.
• ANOVA, multiple classification analysis (SPSS)

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Trip Generation Attractions

• Attraction rates often used x trips per
  employee by NCAIS or SIC Equivalency table
  (http//www.census.gov/epcd/www/naicstab.htm)
• Attractions from households, persons or special
  generator units
• Avoid procedure with additive constants trips
  from empty zones.
• Borrow rates or develop from survey
• Some times area type are used.
• Sometimes need to stratify by type of
  job/income/pay level.

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Trip Generation Special Generators

• Areas not handled well by the models standard
  rates.
• Special rates for things like
• Airports
• Shopping centers/malls
• Amusement and other parks
• Many others
• Might not change over time
• Minimize the use of these

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Trip Generation Implementation

• Could be done with spreadsheet Many dangers
  here.
• Recommend implementation through model script or
  program
• GISDK for TransCAD
• C, VB (compiled or WSH), FORTRAN

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QUESTIONS?

• ?