Improvements and Improvements and Innovations in TDFInnovations in TDF

CE 451/551CE 451/551

Source: NHI course on Travel Demand Forecasting (152054A) Chapter 12

Review of the Four-Step Review of the Four-Step ProcessProcess

What was the original intention of the TDF What was the original intention of the TDF process?process?

What has changed?What has changed?

What questions are we trying to answer now?What questions are we trying to answer now?

Is the current model structure capable of Is the current model structure capable of addressing these issues?addressing these issues?

What are some of the weaknesses in the models?What are some of the weaknesses in the models?

Trip Generation

Trip Distribution

Mode Choice

Trip Assignment

Accessibility and Land Use Character

Land Use Allocation and Forecasting Procedures

Non-motorized Transportation PEF BEF LOS

Multimodal Travel Time and Impedance

Dynamic Traffic Assignment and Simulation Modeling

Operational Improvements

Improved Speed Models

Improved Travel Surveys and Data Collection (all steps)

Trip Chaining Behavior and Activity Modeling

Feedback Analysis

Time-of-Day Models and Peak Spreading

Improvements to Improvements to Traditional Four-Step Traditional Four-Step ModelingModeling

What are we currently What are we currently working with?working with?

4-Step Process is Current State 4-Step Process is Current State of the Practice for TDF and of the Practice for TDF and Policy Analysis.Policy Analysis.

Basics Developed 1950’s and Basics Developed 1950’s and 1960’s1960’s

Post-War Expansion Period in Post-War Expansion Period in U.S.U.S.– Urban Population GrowthUrban Population Growth– Motor Vehicles More UbiquitousMotor Vehicles More Ubiquitous– Suburban Sprawling StartingSuburban Sprawling Starting www.fortunecity.com/tinpan/parton/2/1950s.html

blogs.ipswitch.com/archives/2005/08/

http://www.allposters.com/

Focused on Focused on Infrastructure Infrastructure DevelopmentDevelopment Interstate Construction EraInterstate Construction Era

– Where to Build Them?Where to Build Them?– How Many Lanes?How Many Lanes?

Straight Forward Planning ContextStraight Forward Planning Context Coarse Forecasting Procedures Coarse Forecasting Procedures

SufficientSufficient Population Increases and So Do Population Increases and So Do

Trips.Trips.– Just figure out where the facilities Just figure out where the facilities

were needed. were needed.

Times Are Changing…Times Are Changing…

1970’s Transportation 1970’s Transportation Systems Management Systems Management PromotedPromoted

1980’s Travel Demand 1980’s Travel Demand Management ProposedManagement Proposed

We now embrace a wider We now embrace a wider range of Transportation range of Transportation Control Measures.Control Measures.

These measures are These measures are increasingly more increasingly more sophisticated.sophisticated.

The trip based 4-step The trip based 4-step procedures previously procedures previously developed are quickly developed are quickly becoming insufficient. becoming insufficient.

Advantages of 4-Step Advantages of 4-Step ProcessProcess The simplified process made forecasting practical The simplified process made forecasting practical

using:using:– Standard Survey MethodsStandard Survey Methods– Census and other Data SetsCensus and other Data Sets– Utilizing existing computational capabilitiesUtilizing existing computational capabilities

It Also Facilitated Quantitative Analysis of Travel It Also Facilitated Quantitative Analysis of Travel Demand (which is based on the complexities of travel Demand (which is based on the complexities of travel behavior)behavior)

Urban Transportation Urban Transportation Planning SystemPlanning System UTPS* Standard Analysis UTPS* Standard Analysis

PackagePackage Led to PC-based Programs Led to PC-based Programs

PlanPacPlanPac– Initially Developed by BPRInitially Developed by BPR– Enhanced by FHWAEnhanced by FHWA

These have made the These have made the forecasting procedure forecasting procedure affordable to most any affordable to most any MPOMPO

Still talking circa 1960’s Still talking circa 1960’s and 1970’sand 1970’s

*Not the University of Toronto Pagan Society!

Recognized Internal Recognized Internal InconsistenciesInconsistencies

Productions and Attractions Productions and Attractions typically do not match and typically do not match and require adjustment.require adjustment.

Travel Times used for Trip Travel Times used for Trip Distribution are often different Distribution are often different than those used for than those used for Assignment.Assignment.

External Analysis DeficienciesExternal Analysis Deficiencies Peak Hour LimitationsPeak Hour Limitations Need for Special GeneratorsNeed for Special Generators Estimation of Intrazonal Travel Estimation of Intrazonal Travel

TimesTimes Determination of the Speed Determination of the Speed

Volume RelationshipVolume Relationship K-Factor useK-Factor use

Data InefficiencyData Inefficiency

When disaggregate models were When disaggregate models were first proposed in the 1970’s it was first proposed in the 1970’s it was argued the 4-step process was not argued the 4-step process was not data efficientdata efficient– Remember…Computing Power Remember…Computing Power

Limited and Statistical Theory for Limited and Statistical Theory for model estimation was in infancy. model estimation was in infancy.

– Aggregation of HH and Emp. data to Aggregation of HH and Emp. data to TAZTAZ

Behavioral FoundationBehavioral Foundation

Assumptions can be problematicAssumptions can be problematic Trip Generation Model Example:Trip Generation Model Example:

– Cross-class and regression assume #trips Cross-class and regression assume #trips generated is function of persons in HH and generated is function of persons in HH and vehicles available. In reality, income is a vehicles available. In reality, income is a more representative variable for more representative variable for estimating tripsestimating trips

Additional Additional Limitations/IssuesLimitations/Issues Intersection Delay Typically Intersection Delay Typically

IgnoredIgnored– All Delay is assumed on linksAll Delay is assumed on links– Highly Coordinated Signal Highly Coordinated Signal

SystemsSystems– ITS TechnologyITS Technology– In-vehicle Congestion InfoIn-vehicle Congestion Info

Assumption Travel Only Assumption Travel Only Occurs on the NetworkOccurs on the Network– Over-Simplified NetworkOver-Simplified Network– Centroids and Centroid Centroids and Centroid

Connectors for local travelConnectors for local travel– For air pollution studies off For air pollution studies off

network travel must be addednetwork travel must be added Simplified CapacitiesSimplified Capacities

– Only based on number of Only based on number of lanes and side-friction (area lanes and side-friction (area type)type)

– Not considered – Truck Not considered – Truck movements, terrain, geometrymovements, terrain, geometry

Additional Additional Limitations/IssuesLimitations/Issues

Time of Day VariationsTime of Day Variations– Typically 10% Rule of ThumbTypically 10% Rule of Thumb– Variations are more complex Variations are more complex

in realityin reality– A small variation by 1%-2% A small variation by 1%-2%

could make a big difference.could make a big difference. Emphasis on Peak HourEmphasis on Peak Hour

– Forecasts are average Forecasts are average weekday.weekday.

– More projects are using More projects are using “peak-period” forecasts“peak-period” forecasts

– Derived by hand calculationsDerived by hand calculations

Trip Generation

Trip Distribution

Mode Choice

Trip Assignment

Accessibility and Land Use Character

Land Use Allocation and Forecasting Procedures

Non-motorized Transportation PEF BEF LOS

Multimodal Travel Time and Impedance

Dynamic Traffic Assignment and Simulation Modeling

Operational Improvements

Improved Speed Models

Improved Travel Surveys and Data Collection (all steps)

Trip Chaining Behavior and Activity Modeling

Feedback Analysis

Time-of-Day Models and Peak Spreading

Improvements to Improvements to Traditional Four-Step Traditional Four-Step ModelingModeling

How Can Models Be How Can Models Be Improved?Improved?

Transportation models are being called upon to Transportation models are being called upon to provide forecasts for a complex set of problems that provide forecasts for a complex set of problems that in some cases can go beyond their capabilities and in some cases can go beyond their capabilities and original purposeoriginal purpose

Better DataBetter Data– All models are based on data about travel patterns All models are based on data about travel patterns

and behavior. and behavior.

– If these data are out-of-date, incomplete or inaccurate If these data are out-of-date, incomplete or inaccurate … the results will be poor no matter how good the … the results will be poor no matter how good the

models aremodels are – One of the most effective ways of improving model One of the most effective ways of improving model

accuracy and value is to have a good basis of recent accuracy and value is to have a good basis of recent data to use to calibrate the models and to provide for data to use to calibrate the models and to provide for checks of their accuracychecks of their accuracy

How Can Models Be How Can Models Be Improved?Improved? Inclusion of Other ModesInclusion of Other Modes

– TransitTransit– BicyclingBicycling– WalkingWalking

Better Auto Occupancy ModelsBetter Auto Occupancy Models– Sensitive to Policy Issues such as Sensitive to Policy Issues such as

Parking CostsParking Costs– Ride SharingRide Sharing

Use More Trip PurposesUse More Trip Purposes– May Help to Address Complex HH Trip May Help to Address Complex HH Trip

PatternsPatterns– Trip ChainingTrip Chaining– More Sensitive Trip Generation Factors More Sensitive Trip Generation Factors

How Can Models Be How Can Models Be Improved?Improved? Better Representation of Land AccessBetter Representation of Land Access

– Smaller ZonesSmaller Zones– More ConnectorsMore Connectors– Land use policies that facilitate transit use Land use policies that facilitate transit use

or that provide high quality site design or that provide high quality site design with good pedestrian access are not well with good pedestrian access are not well represented in the transportation models. represented in the transportation models.

Trip Distribution and CostsTrip Distribution and Costs– Trip distribution models should use a Trip distribution models should use a

generalized measure of distance that generalized measure of distance that includes costs of travel by different means includes costs of travel by different means including parking costs. including parking costs.

How Can Models Be How Can Models Be Improved?Improved? Add Land Use Feedback Add Land Use Feedback

– Gain a better representation of the interaction of land Gain a better representation of the interaction of land use and travel demand.use and travel demand.

– Land use simulation models should be added to the Land use simulation models should be added to the sequence of models to help to determine how a sequence of models to help to determine how a proposed transportation system will lead to land use proposed transportation system will lead to land use changes. changes.

How Can Models Be How Can Models Be Improved?Improved? Add intersection delays Add intersection delays

– In an urban traffic network most In an urban traffic network most delay is encountered at traffic delay is encountered at traffic signals or stop signssignals or stop signs

– Travel forecasting models should Travel forecasting models should include routines that calculate the include routines that calculate the delay encountered at intersections delay encountered at intersections

– Feedback Loops with Congested Feedback Loops with Congested Travel Time.Travel Time.

TMPI Outreach and Technical Assistance

• Review panel to direct program

• Conferences

• Internet home page

• Clearinghouse

• Technical assistance from experts in the field

• Training centers

• Newsletters

TRANSIMS

TRansportation ANalysis and SIMulation Systems (TRANSIMS)

Components:– Individual household and travelers– Micro-simulation– Detailed transportation network– Air quality– Analyst toolbox

Parting StatementsParting Statements

no single model system is suited for all no single model system is suited for all study objectives study objectives

The trip-based, four-step procedure The trip-based, four-step procedure continues to be an effective demand continues to be an effective demand forecasting procedure for certain types of forecasting procedure for certain types of problems, yet, current policy contexts call problems, yet, current policy contexts call for alternative modelsfor alternative models

The array of transportation planning tools The array of transportation planning tools available to policy makers needs to be available to policy makers needs to be expanded. expanded.