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FDOT Systems PlanningWhite Paper

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

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Presentation Overview

Purpose and Need

Reviewers

Recommendation Checklist

Delineating TAZs in the Base-Year Model

Future-Year TAZ Considerations

Splitting TAZs

Topics Requiring Further Research

Where to Find the Paper

Discussion

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Purpose and Need

Purpose

• Provide modelers within Florida detailed guidance on a recommended approach to delineating TAZs

• Applicable to new travel demand models, or to further refine existing travel demand models

Need

• More realistic representation of transit access inPublic Transport (PT)

• Improved model accuracy for both highwayand transit models

• Consistent approach for the modeling and planning community in the State

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Reviewers

FDOT

FHWA

MTF Model Advancement Committee

MTF Data Committee

Other interested parties outside Florida

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Recommendation Checklist

The number of people per TAZ should be greater than 1,200, but less than 3,000 for the base- and future-yearsEach TAZ yields less than 15,000 person trips in thebase- and future-yearsThe size of each TAZ is between 0.25 to one squaremile in areaThere is a logical number of intrazonal trips in each zone based on the mix and density of the land useThere are no irregular-shaped TAZsEach centroid connector loads less than 10,000 to 15,000 vehicles per day in the base- and future-yearThe study area is large enough so that nearly all (over 90 percent) of the trips begin and end within the study area

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Recommendation Checklist (continued)

The TAZ structure is compatible with thebase- and future-year highway and transit network

The centroid connectors represent realistic access points to the highway network

Transit access is represented realistically

The TAZ structure is compatible with census, physical, political, and planning district/sector boundaries

The TAZs are based on homogeneous land uses, when feasible, in both the base- and future-year and consider future DRIs

Special generators and freight generators/attractors are isolated within their own TAZ

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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

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

Size of zones depends on intended use of model• Large-sized zones for system or statewide planning

− Statewide models

− TAZs can be larger than the arterial grid

− Up to approximately 20,000 persons per zone

• Medium-sized zones for arterial 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

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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

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Delineating TAZs in the Base-Year Model Socioeconomic Data

Homogeneousland uses,where feasible

Special generators

Trips per zone

Developments ofregional impact

Figure 3.10  Delineating TAZs Based on Clusters of Similar Land Uses

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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

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Delineating TAZs in the Base-Year Model Centroid Connectors

Represent realistic roadway and transit access

Should not cross man-made or natural barriers

Include a sufficient number of centroid connectors to avoid loading too many trips 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, the 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

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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

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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 a list of thenew zone numbers that were split from the originalzone numbers

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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

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Future Year TAZ ConsiderationsPopulation and Trips per Zone

Anything more than 15,000 trips per day or 1,200 to 3,000 people per TAZ exceeds the 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 the future-year land use, it may verywell push the population or daily trips over the thresholds noted above

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Splitting TAZs

Network data impacts

Socioeconomicdata impacts

Boundary shiftsand zone aggregations

Zones beyondmodel boundary

Revalidation

Figure 5.1  Splitting Household Data into New TAZs

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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

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Where to Find the Paper

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

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Discussion

Questions or Comments?