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The Four-step Travel Model The Four-step Travel Model

GEOG 111 & 211A – Fall 2004

October 14

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OutlineOutline

Background Role of Simulation General Process Example of Most Popular Simulation Model Examples of Other Ideas

Summary

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NeedsNeeds

Identify Projects for the RegionUse Formal & Accepted Technique(s) to

Estimate Project ImpactsSimulate the Region for the Next 20 YearsCreate Scenarios for BEFORE and AFTER

a Project or Group of Projects

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Create a Comprehensive Plan of how we want the area to be in the future

Propose projects designed to achieve the goals of the Comprehensive Plan

Test Scenarios implementing different projects and forecast their effects

Determine what projects should be continued to next stage

Present recommendations to decision makers

How Do we use Simulation How Do we use Simulation Models?Models?

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Project TypesProject Types

New Highways (e.g., bypass-ring roads)New Management Activities (e.g., park & ride,

signal systems )New Land Uses (e.g., a new industry, a new

residential neighborhood)New Technologies??????? (maybe in

management)

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The ContextThe Context

Urban Transportation Planning System (UTPS) & Urban Transportation Modeling System

TEA 21 made it also A Statewide Transportation Planning System

Technology should be added (see Pennplan) Associate quantitative estimates with performance

measures as in the monitoring part (see PennPlan) Four-step scheme followed today in many MPOs Four-step travel model is limited but popular!

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Goals andobjectives

SurveillanceReappraisalProcedural developmentServiceAnnual report

Continuing elements

Policy andtechnical development

Develop immediateaction plan

PennDOTMPOsTMAsLDDsLocal gov’tsCitizen participation

Transportationorganizations

Plan implementation

Land useTrip generationTrip distributionModal splitTraffic assign.

Calibrate models

PopulationLand useEconomicTrafficRevenues

Areawideforecast

= Part of the Sequential Demand Forecasting Process

Develop alternativesApply models

Land useTrip generationTrip distributionMode choiceTraffic assign.

Plan testing, evaluationand selection

Analysis of futurealternative systems

PopulationLand useEconomic activityTransportation systemTravel volumesTerminal and transfer

facilities status & useFinancial resourcesCommunity values

Inventories anddata collection

DATA

Typical Process in Long Range Planning

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The Sequential Forecasting Process & The Sequential Forecasting Process & the Urban Transportation Planning System (UTPS)the Urban Transportation Planning System (UTPS)[adapted from Papacostas & Prevedouros, 1993][adapted from Papacostas & Prevedouros, 1993]

Transportationsystem

specification

NetworkAssignment

ModeChoice

TripGeneration

TripDistribution

Land use and socioeconomic

projections

Direct (user)Impacts

4-STEP

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Four step in large MPOsFour step in large MPOs

Inventory of facilitiesOpportunity to think strategicallyShow the impact of projects on air qualityProvide report of emissions inventoryTool for policy assessmentPSRC example follows!

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Forecast future development (business, roadways, and housing)

Model the area’s traffic network Estimate model of the area’s traffic network in the future Make changes to network characteristics in the future

model Compare network performance under different scenarios

of project development

What Other Steps Are Required?What Other Steps Are Required?

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UTPS OutlineUTPS OutlineUTPS OutlineUTPS Outline Review the Data Inventory for a Region Review one Procedure to Predict Future Volumes on a

Highway Summarize the Method Known as UTPS Questions

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UTPS 4-step Travel ModelUTPS 4-step Travel ModelUTPS 4-step Travel ModelUTPS 4-step Travel Model

Trip GenerationTrip DistributionModal SplitTraffic Assignment

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Data (Inventory)Data (Inventory)Data (Inventory)Data (Inventory) Area of study definition & traffic analysis zones Area of study description (highways, facilities, zoning,

rules/regulations) Who are the residents? (age, gender, education,

employment, income of residents) Where do people leave? Where do people work, shop, etc? Highway characteristics Other information (plans for rezoning)

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Travel ModelTravel ModelTravel ModelTravel Model Urban Travel Model (‘60s)

– Also known as the Four - Step Process– A methodology to model traffic on a network

General planning & programming Land use forecasting (where will residences and stores be?) Four Steps:

– Trip Generation Estimate Person Trips for each TAZ

– Trip Distribution Distribute Person Trips from TAZ to TAZ

– Mode Choice Convert Person Trips to Vehicle Trips

– Traffic Assignment Assign Vehicles to the Network

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Key Concepts of 4-stepKey Concepts of 4-stepKey Concepts of 4-stepKey Concepts of 4-step TAZ: Traffic Analysis Zone

– TAZ= a common sense subdivision of the study area– TAZs are used in trip generation and trip distribution– TAZs may be any shape or size, but US Census Blocks,

Block Groups, and Tracts are often used (class: WHY?)

Block Block Group Tract

i.e., a city block

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8-Zone Study Area 8-Zone Study Area with Traffic Analysis Zones (TAZs)with Traffic Analysis Zones (TAZs)

8-Zone Study Area

1

87

4 5

6

32

z

z = all zones outside study area

x = TAZ designations study area boundary

TAZ boundaries

Legend:

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Key Concepts of UTPSKey Concepts of UTPSKey Concepts of UTPSKey Concepts of UTPS Centroid

– Every TAZ (Gate and Internal) has a centroid, usually placed roughly at the geographic center of the TAZ

– All trips to or from a TAZ are assumed to start or end at the centroid

Discussion– Why do we use TAZs and centroids to model trips?

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Key Concepts of UTPSKey Concepts of UTPSKey Concepts of UTPSKey Concepts of UTPS Gate TAZs

– TAZs placed outside the Study Area where major roads cross the boundaries of the study area

– Used to model External Trips (i.e., trips with an origin or destination) Note: Do we care when OD is outside the study area?

– Gate TAZs represent all areas outside of the study area

(Study Area)

Gate TAZ

Network

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Network & Links Numbered

1

23 4

5 6 78 9 10 11 12

13 14 1516 17

18 1920 21

22

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Example: Computer schematic representation

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1

2

3 4 5 6 7

8 9 10 11 12 13

14 15 16 17 18

19 20 21

22

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Network and Nodes Numbered

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23

Gate TAZ

Centroid

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Land Use/Economic AnalysisLand Use/Economic Analysis

Considers general trendsAllocates population to geographic

subdivisionsAssigns land usesEach TAZ contains “observed” numbers

for today’s analysis and predicted numbers for forecasting

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OUTPUT = a map with TAZ’s and OUTPUT = a map with TAZ’s and their characteristics – households, their characteristics – households, businesses, employersbusinesses, employers

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Trip Generation ProcessTrip Generation ProcessTrip Generation ProcessTrip Generation Process Collect Data, usually by Surveys and Census

– Sociodemographic Data and Travel Behavior Data

Create a Trip Generation Model (e.g., regression) Estimate the number of Productions and Attractions for

each TAZ, by Trip Purpose Balance Productions and Attractions for each Trip Purpose

– Total number of Productions and Attractions must be equal for each Trip Purpose

– We will discuss balancing later

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Trip Generation ModelsTrip Generation ModelsTrip Generation ModelsTrip Generation Models Regression Models

– Explanatory Variables are used to predict trip generation rates, usually by Multiple Regression

Trip Rate Analysis– Average trip generation rates are associated with different

trip generators or land uses

Cross - Classification / Category Analysis– Average trip generation rates are associated with different

trip generators or land uses as a function of generator or land use attributes

Models may be TAZ, Household, or Person - Based

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ITE Trip Generation ManualITE Trip Generation ManualITE Trip Generation ManualITE Trip Generation Manual Trip Rate Analysis Model

– Univariate regression for trip generation– Primarily for Businesses– Explanatory variables are usually number of employees or

square footage– Models developed using data from national averages and

numerous studies from around the US

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Possible geographic detail in trip generation with GIS & business data

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Typical output from trip generation

OUTPUT

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Trip DistributionTrip DistributionTrip DistributionTrip Distribution Convert Production and Attraction Tables into Origin -

Destination (O - D) Matrices

Destinations

123456Sum

Origins 1 2 3 4 5 6 SumT11 T12 T13 T14 T15 T16 O1

T21 T22 T23 T24 T25 T26 O2

T31 T32 T33 T34 T35 T36 O3

T41 T42 T43 T44 T45 T46 O4

T51 T52 T53 T54 T55 T56 O5

T61 T62 T63 T64 T65 T66 O6

D1 D2 D3 D4 D5 D6

TAZ P1513261881393

A2265522693

123456Sum

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Trip Distribution, MethodologyTrip Distribution, MethodologyTrip Distribution, MethodologyTrip Distribution, Methodology

General Equation:

– Tij = Ti P(Tj)Tij = calculated trips from zone i to zone jTi = total trips originating at zone iP(Tj) = probability measure that trips will be attracted to

zone j

Constraints:Singly Constrained

– Sumi Tij = Dj OR Sumj Tij = OiDoubly Constrained

– Sumi Tij = Dj AND Sumj Tij = Oi

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Trip Distribution Models Trip Distribution Models ExampleExampleTrip Distribution Models Trip Distribution Models ExampleExample

Gravity Model Tij is:Tij = trips from zone i to zone j =

Ti = total trips originating at zone iAj = attraction factor at jAx = attraction factor at any zone xCij = travel friction from i to j expressed as a generalized cost

functionCix = travel friction from i to any zone x expressed as a

generalized cost functiona = friction exponent or restraining influence

Sum (Ax / Cix)a

TiAj / Cij a

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Gravity Model ProcessGravity Model ProcessGravity Model ProcessGravity Model Process Create Shortest Path Matrix

– How: Minimize Link Cost among Centroids

Estimate Friction Factor Parameters– How: Function of Trip Length Characteristics by Trip

Purpose

Calculate Friction Factor Matrix Convert Productions and Attractions to Origins and

Destinations Calculate Origin - Destination Matrix Enforce Constraints on O - D Matrix

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Shortest Path MatrixShortest Path MatrixShortest Path MatrixShortest Path Matrix Matrix of Minimum Generalized Cost from any Zone i to

any Zone j– Distance, Time, Monetary Cost, Waiting Time, Transfer

Time, etc.. may be used in Generalized Cost– Time or Distance Often Used– Matrix Not Necessarily

Symmetric (Effect of

One - Way Streets)

TAZ ID

123456

TAZID 1 2 3 4 5 6

C11 C12 C13 C14 C15 C16 C21 C22 C23 C24 C25 C26 C31 C32 C33 C34 C35 C36 C41 C42 C43 C44 C45 C46 C51 C52 C53 C54 C55 C56 C61 C62 C63 C64 C65 C66

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O - D Matrix CalculationO - D Matrix CalculationO - D Matrix CalculationO - D Matrix Calculation Calculate Initial Matrix By Gravity Equation, by Trip

Purpose– Each Cell has a Different Friction, Found in the

Corresponding Cell of the Friction Factor Matrix

Enforce Constraints in Iterative Process– Sum of Trips in Row i Must Equal Origins of TAZ i– Sum of Trips in Column j Must Equal Destinations of TAZ j– Iterate Until No Adjustments Required

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O - D Matrix Example:O - D Matrix Example:O - D Matrix Example:O - D Matrix Example:

Destinations

123456Sum

Origins 1 2 3 4 5 6 SumT11 T12 T13 T14 T15 T16 O1

T21 T22 T23 T24 T25 T26 O2

T31 T32 T33 T34 T35 T36 O3

T41 T42 T43 T44 T45 T46 O4

T51 T52 T53 T54 T55 T56 O5

T61 T62 T63 T64 T65 T66 O6

D1 D2 D3 D4 D5 D6

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Final O - D MatrixFinal O - D MatrixFinal O - D MatrixFinal O - D Matrix Combine (Add) O - D Matrices for Various Trip Purposes Scale Matrix for Peak Hour

– Scale by Percent of Daily Trips Made in the Peak Hour– 0.1 Often Used

Scale Matrix for Vehicle Trips– Scale by Inverse of Ridership Ratio to Convert Person Trips

to Vehicle Trips– 0.95 to 1 Often Used

Note: Other Mode Split Process / Models using Discrete Choice may be More Accurate

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OUTPUT = the trip interchange OUTPUT = the trip interchange matrix and the shortest path treesmatrix and the shortest path trees

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Modal SplitModal SplitModal SplitModal Split Use a model to convert trips into vehicle trips Usually public transportation versus private car Nomographs, Regression methods, Microeconomic

Regression methods Stated Preference (conjoint measurement) techniques for

hypothetical options Traveler objective and subjective constraints in selecting a

mode

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OUTPUT = a trip interchange matrix OUTPUT = a trip interchange matrix for each mode: car, public for each mode: car, public transportation, could also be transportation, could also be pedestrian but not usualpedestrian but not usual

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Traffic AssignmentTraffic AssignmentTraffic AssignmentTraffic Assignment Fourth Step in UTPS Modeling Inputs:

– Peak Hour, Passenger Vehicle Origin - Destination (O - D) Matrix

– NetworkTravel Time, Capacity, Direction

Outputs:– Peak Hour Volumes, Estimated Travel Times, and Volume

to Capacity Ratios

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Roadway Performance FunctionsRoadway Performance FunctionsRoadway Performance FunctionsRoadway Performance Functions Traffic Flow and Travel Time

Traffic Flow Traffic Flow

Linear Relationship Non-Linear Relationship

Rou

te T

rave

l Tim

e

Cap

acity

Free-FlowTravel Time

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Assignment MethodsAssignment MethodsAssignment MethodsAssignment Methods All or Nothing

– All traffic from zone i to zone j uses the (initially) minimal travel time path

– Roadway performance not used

System Equilibrium– Assignment is performed such that total system travel time is

minimized (UPS, Fed-EX).

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Assignment MethodsAssignment MethodsAssignment MethodsAssignment Methods User Equilibrium

– Travel time from zone i to zone j cannot be decreased by using an alternate route

– Roadway performance used

Stochastic User Equilibrium– Same as User Equilibrium but accounts for user variability

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Dynamic Assignment MethodsDynamic Assignment MethodsDynamic Assignment MethodsDynamic Assignment Methods Assign Traffic by Time of Day

– Estimate origins & destinations by time of day– Apply an equilibrium method– Sometimes incorporate departure time choice– Sometimes incorporate system performance characteristics

See also page 288 of Meyer & Miller, 2001 textbook

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OUTPUT = traffic volumes (cars per OUTPUT = traffic volumes (cars per hour) on each road, travel times on hour) on each road, travel times on each link, congestion levelseach link, congestion levels

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Planning 4-step Procedure SummaryPlanning 4-step Procedure SummaryPlanning 4-step Procedure SummaryPlanning 4-step Procedure Summary Land Use and Economics Trip Generation Trip Distribution Modal Split Traffic Assignment Main Input=Sociodemographics of study area Main Output=Traffic volumes and level of service on

roads Secondary input-output (many depends on application and

software)

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Output from traffic assignment

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Output from traffic assignment

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Questions?Questions?Questions?Questions?