Transportation Economics/Network growth

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Network Growth

Contents

[edit] Surface transportation networks come in layers

  • 11 Places
  • 10 Trip Ends
  • 9 End to End Trip
  • 8 Driver/Passenger
  • 7 Service (Vehicle & Schedule)
  • 6 Signs and Signals
  • 5 Markings
  • 4 Pavement Surface
  • 3 Structure (Earth & Pavement and Bridges)
  • 2 Alignment (Vertical and Horizontal)
  • 1 Right-Of-Way
  • 0 Space

This is analogous to the OSI Reference Model used for the Internet

  • 7 Application Layer - The Application Layer is the level of the protocol hierarchy where user-accessed network processes reside.
  • 6 Presentation Layer - For cooperating applications to exchange data, they must agree about how data is represented. In OSI, this layer provides standard data presentation routines.
  • 5 Session Layer As with the Presentation Layer, the Session Layer is not identifiable as a separate layer in the TCP/IP protocol hierarchy. The OSI Session Layer manages the sessions (connection) between cooperating applications.
  • 4 Transport Layer - Much of our discussion of TCP/IP is directed to the protocols that occur in the Transport Layer. The Transport Layer in the OSI reference model guarantees that the receiver gets the data exactly as it was sent.
  • 3 Network Layer The Network Layer manages connections across the network and isolates the upper layer protocols from the details of the underlying network. The Internet Protocol (IP), which isolates the upper layers from the underlying network and handles the addressing and delivery of data, is usually described as TCP/IP's Network Layer.
  • 2 Data Link Layer The reliable delivery of data across the underlying physical network is handled by the Data Link Layer.
  • 1 Physical Layer The Physical Layer defines the characteristics of the hardware needed to carry the data transmission signal. Features such as voltage levels, and the number and location of interface pins, are defined in this layer.

[edit] Where Does Intelligence Lie

  • Smart Networks, Dumb Packets/Vehicles (Railroads, Telephone)
  • Smart Packets/Vehicles, Dumb Networks (Roads, Internet)

Important to resolve this in network design

[edit] Network Design vs. Network Growth

Network Design Problem (NDP) tries to determine “optimal” network according to some criteria (Z). - Normative

E.g. Maximize Z, subject to some constraints.

Network Growth Problem tries to predict actual network according to observed or hypothesized behaviors. - Positive

[edit] Questions

  • Why do networks expand and contract?
  • Do networks self-organize into hierarchies?
  • Are roads an emergent property?
  • Can investment rules predict location of network expansions and contractions?
  • How can this improved knowledge help in planning transportation networks?
  • To what extent do changes in travel demand, population, income and demographic drive changes in supply?
  • Can we model and predict the spatially specific decisions on infrastructure improvements?


[edit] Network Growth

  • Depends on existing and forecast transportation demand
  • Depends on existing transportation supply
  • Network can be viewed as output of a production function: N = f( D, S)

Over the long term, we expect networks to grow in the fashion of an S-Curve as discussed in the Lesson on Positive Externalities


[edit] How networks change with time

  • Nodes: Added, Deleted, Expanded, Contracted
  • Links: Added, Deleted, Expanded, Contracted
  • Flows: Increase, Decrease

[edit] The Node Formation Problem

  • Christaller’s Central Place Theory (CPT) sought to answer: How are urban settlements spaced, more specifically, what rules determine the size, number and distribution of towns? Christaller’s model made a number of idealizing assumptions, especially regarding the ubiquity of transport services, in essence, assuming the network problem away. His world was a largely undifferentiated plain (purchasing power was spread equally in all directions), with central places (market towns) that served local needs. The plain was demarcated with a series of hexagons (which approximated circles without gaps or overlaps), the center of which would be a central place. However some central places were more important than others because those central places had more activities. Some activities (goods and services) would be located nearer consumers, and have small market areas (for example a convenience store) others would have larger market areas to achieve economies of scale (such as warehouses).

[edit] Central Place & Network Hierarchy

Network Hierarchy is much like Central Places (Downtown Minneapolis, Suburban Activity Centers (e.g. Bloomington, Edina, Eden Prarie), Local Activity Centers (e.g. Dinkytown, Stadium Village, Midway), Neighborhood Centers (4th Avenue & 8th Street SE).

Central Places occur both within and between cities. Hierarchy: Minneapolis-St. Paul; Duluth, St. Cloud, Rochester; Morris, Brainerd, Marshall, etc.; International Falls, etc.

[edit] Exercise

[edit] Further reading

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