Transportation Planning - Zoning Systems

Transportation Planning - Zoning Systems

1 Zoning Systems

1.1 Basic Definitions

• Traffic Analysis Zones (TAZs)

• Centroids

• Origins

• Destinations

• Trip production

• Trip attraction

• Directional trip production

• Directional trip attraction

1.2 Transportation Analysis Zones (TAZs)

Socioeconomic data, including household and employment data, for a study area are usually organized into geographic units called traffic analysis zones.

TAZ boundaries are usually major roadways, jurisdictional borders, and geographic boundaries and are defined by homogeneous land uses to the extent possible.

The number and size of TAZs can vary but should generally obey the following rules of thumb when possible (guidelines of NCHRP Report 716 of United States):

• The number of residents per TAZ should be greater than 1,200, but less than 3,000;

• Each TAZ should yield less than 15,000 person travel trips per day;

• The size of each TAZ should be from one-quarter to one square mile (0.6475 - 2.59 km2) in area.

1.3 Centroids

• Each TAZ has a centroid, which is a point on the model network that represents all travel origins and destinations in a zone.

• Zone centroids should be located in the center of activity (not necessarily coincident with the geographic center) of the zone, using land-use maps, aerial photographs, and local knowledge.

• Each centroid serves as a travel trip loading point to the highways and transit systems and, therefore, must be connected to the model network.

1.4 Zoning Design Guidelines

• Zoning system is used to aggregate individual households and premises into manageable chunks for travel demand modelling purposes.

  • The main dimensions of a zoning system are the number of zones and their sizes.

  • The greater the number of zones, the smaller they can be to cover the same study area.

  • It is common practice to develop a zoning system specifically for each study and decision-making context.

• Some tips for choosing study area:

  In choosing the study area one must consider the decision-making context, the schemes to be modelled, and the nature of the trips of interest: mandatory, optional, long or short distance, and so on.

  • For strategic studies one would like to define the study area so that the majority of trips have their origin and destination inside it; however, this may not be possible for smaller urban areas.

  • For traffic control and management studies in local areas what matters is whether it is possible to model changes to these trips arising as a result of new schemes.

  • The study area should be somewhat bigger than the specific area of interest covering the schemes to be considered.

• Opportunities for re-routing, changes in destination and so on, must be allowed for, and we would like to model their effects as part of the study area itself.

1.5 Denotation

\(O_i\): Number of directional travel trips produced at zone \(i\) (\(i=1,2,\cdots, n\) during a given period (i.e., centroid \(i\)).

\(D_j\): Number of directional travel trips attracted to zone \(j\) (\(j=1,2,\cdots, n\) during a given period (i.e., centroid \(j\)).

\(\big[T_{ij} \big]_{n \times n}\): Number of travel trips from origin \(i\) (i.e., zone or centroid \(i\)) to destination \(j\) (i.e., zone or centroid \(j\)) during a given period.

Two balance equations hold:

\[\begin{align*} O_i = \sum_{j=1}^{n} T_{ij}, \quad \forall i=1,2,\cdots, n \\ D_j = \sum_{i=1}^{n} T_{ij}, \quad \forall j=1,2,\cdots, n \end{align*} \]

One main purpose of travel demand modelling is to predict/estimate the origin-destination (O-D) demand matrix \(T\) for a planning year from base-year socioeconomic data.

Reference

[1] J. de D. Ortúzar S. and L. G. Willumsen, "3.5 Network and Zoning Systems", in Modelling Transport, Fourth edition. Chichester, West Sussex, United Kingdom: John Wiley & Sons, 2011, p.p. 128-131.

[2] "3.2 Socioeconomic Data and Transportation Analysis Zones", in Travel Demand Forecasting: Parameters and Techniques. Washington, D.C: National Academies Press, 2012, p.p. 14-17.