transportation leadership you can trust. fdot systems planning white paper a recommended approach to...
TRANSCRIPT
Transportation leadership you can trust.
FDOT Systems PlanningWhite Paper
A Recommended Approach to DelineatingA Recommended Approach to DelineatingTraffic Analysis Zones in FloridaTraffic Analysis Zones in Florida
2
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
3
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
4
Reviewers
FDOT
FHWA
MTF Model Advancement Committee
MTF Data Committee
Other interested parties outside Florida
5
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
6
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
7
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
8
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
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16
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
17
Splitting TAZs
Network data impacts
Socioeconomicdata impacts
Boundary shiftsand zone aggregations
Zones beyondmodel boundary
Revalidation
Figure 5.1 Splitting Household Data into New TAZs
18
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
19
Where to Find the Paper
White Paper is on-line at www.fsutmsonline.net
20
Discussion
Questions or Comments?