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TRB Planning Applications ConferenceMay 18, 2009Houston, TX

A Recommended Approach to DelineatingA Recommended Approach to DelineatingTraffic Analysis Zones in FloridaTraffic Analysis Zones in Florida

Presentation OverviewPurpose and Need

Reviewers

Recommendation Checklist

Delineating TAZs

• Base-Year Models

• Future-Year TAZ Considerations

• Splitting TAZs

• Topics Requiring Further Research

Where to Find the Full Paper

Acknowledgements and Discussion

Purpose and Need

Purpose

• Provide modelers within Florida guidance on delineating TAZs

• Applicable both to new travel demand models and refining existing models

Need

• Better represent transit access inCube Voyager’s Public Transport (PT) program

• Improved model accuracy for both highwayand transit models

• Consistent approach for Florida’s modeling and planning community

Reviewers

FDOT

Federal Highway Administration (FHWA)

Florida Model Task Force (MTF)

• MTF Model Advancement Committee

• MTF Data Committee

Other interested parties outside Florida

Recommendation Checklist

Persons per TAZ should be greater than 1,200, but less than 3,000 for all years (base and future)

Each TAZ should yield less than 15,000 person trips in all years

The size of each TAZ should be between 0.25 and one square mile in area

Achieve reasonable number of intrazonal trips in each zone based on mix and density of land use

Minimize irregular-shaped TAZs

Centroid connectors should load less than 10,000 to 15,000 vehicles per day in all years

Recommendation Checklist (Cont’d)

Study areas should be large enough so that nearly all (>90%) of trips begin and end within study area

The TAZ structure should be compatible with highway and transit networks for all years

The centroid connectors should represent true access points to highway network

Transit access should be realistically represented

TAZ structure should be compatible with Census, physical, political, and planning district boundaries

Special generators and freight generators should be isolated within their own TAZ

Delineating TAZs in the Base-Year Model

Zone size and quantity

Boundary compatibility

Socioeconomic data

Access

Centroid connectors

Existing transportationfacilities

TAZ numbering

Figure 3.3  Blocks versus Block Groups versus Census Tracts

Census Tracts

Block Groups (Colored Areas)

Blocks

Delineating TAZs in the Base-Year Model Zone Size and Quantity

Size of zones depends on intended use of model• Larger-sized zones for statewide and systems planning

− Statewide models

− TAZs can be larger than the arterial grid

− Up to approximately 20,000 persons per zone

• Medium-sized zones for major investment planning− Regional or MPO models

− Two or more arterials should not traverse the TAZ in any direction

− Up to approximately 4,000 persons per zone

• Small-sized zones for corridor analysis− Corridor level or subarea models

− TAZs in a corridor or subarea should be more refined

− Should be greater than 1,200, but less than 3,000persons per zone

Delineating TAZs in the Base-Year Model Boundary Compatibility

Physical geography

Census geography

Political geography

Planning district/sector boundaries

Irregular zone geography

Figure 3.1  Delineating TAZs Consistent with the Physical Geography

Figure 3.2  Delineating TAZs Based on Permanent Barriers

Delineating TAZs in the Base-Year Model Socioeconomic Data

Special generators

Trips per zone

Developments ofregional impact

Figure 3.10  Delineating TAZs Based on Clusters of Similar Land Uses

Delineating TAZs in the Base-Year Model Access

Transit access

Freight/intermodal facilities

Figure 3.11  Over-Estimating Walk Access to Transit

Development Development

1 mile 0.5 mile

Over-Estimation More Accurate Estimation

Delineating TAZs in the Base-Year Model Centroid Connectors

Represent realistic roadway and transit access

Should not cross man-made or natural barriers

Include sufficient number of centroid connectors to avoid over-loading to one roadway network link

Do not connect centroid connectors at intersectionsor directly to interstate ramps

When two centroid connectors are connected to the same roadway segment, access points should be separated by a certain distance

Figure 3.20  Placement of Centroid Connectors Relative to Intersectionsand Interstate Ramps

The Wrong Way                        The Right Way

Delineating TAZs in the Base-Year Model Existing Transportation Facilities

Rail lines

Limited access highways

Arterial streets and roadways

Collector streets and roadways

Figure 3.14  Delineating TAZs Based on Transit Access

Delineating TAZs in the Base-Year Model TAZ Numbering

Recommended that TAZ numbers begin with oneand be consecutive

Regional models may set aside a specific range of TAZ numbers for both TAZs and dummy zones for each county

Create TAZ equivalency tables to provide list of new zone numbers split from original zone numbers

Future Year TAZ Considerations

Plannedtransportationcorridors

Developments ofregional impact

Populationand tripsper zone

Figure 4.1  Defining the TAZ Structure Based on Future Corridors

Figure 4.2  Defining the TAZ Structure Based on Future DRI

Future Year TAZ ConsiderationsPopulation and Trips per Zone

Greater than 15,000 trips per day or 1,200 to 3,000 people per TAZ exceeds recommended zone size

• The Census Bureau is currently considering increasing the minimum number of persons per block group (and potentially TAZs) to 1,200 persons (previously 600) or 480 households. The existing maximum thresholds of 3,000 persons and 1,200 households per block group remain unchanged

Often times, a TAZ may not have as many people or generate that many daily trips in the base-year

However, with future-year land use, it may push population or daily trips over the thresholds noted above

Splitting TAZs

Network data impacts

Socioeconomicdata impacts

Boundary shiftsand zone aggregations

Zones beyondmodel boundary

Revalidation

Figure 5.1  Splitting Household Data into New TAZs

Topics Requiring Further Research

Mixed land uses• Delineating TAZs based on homogenous land uses is not

always feasible

• CBDs and neo-traditional developments make it difficult to isolate employees from households

Dynamic subzoning• Potential solution to mixed land use issue

• Includes multiple centroids within one zone; one to represent employment and another to represent households

• Allows different access points onto the network by having one set of centroid connectors for employment and another for households

• Would require further research, including the numberingof subzones

Where to Find the Paper

Full White Paper is on-line at www.fsutmsonline.net

AcknowledgementsFlorida Department of Transportation (FDOT)

• Vidya Mysore, Systems Planning Office (SPO)

• Terry Corkery, SPO

Cambridge Systematics (CS)

• Keli Paul, AICP

• Rob Schiffer, AICP

AECOM Consult

• Dave Schmitt

Discussion

Questions or Comments?

Keli Paul, AICPCambridge Systematics

Senior AssociateTallahassee, FL 32301

850.219.6388kpaul@camsys.com

Terry CorkeryFDOT, Systems Planning OfficeSenior Transportation Modeler

Tallahassee, FL 32399850.414.4900

Terrence.Corkery@dot.state.fl.us