Today we review a seminal paper from over a decade ago that examines the dynamics of road development in a major mid-West American city (Minneapolis-Saint Paul) using a model that combines measures such as travel demand statistics (usually found on Origin Destination studies) with the economics of road pricing or tolls, geographical constraints (such as rivers and mountains) and how these change with newer technology over time (in this case over 20 years). Roads represent both figuratively and physically the link that join the issues addressed in this blog: how traffic is linked to pollution and how pollution is linked to health. Of particular interest is the way that travel demand and road volume capacity (VC) interact with road tolls and the cost of road construction and the resulting revenue that may be used to ease congestion, in addition to the overall design of the road network and design for a major urban area.
“In 1900 there were 240 km of paved road in the United States … and this total had increased to 6,400,000 by 2000 …with virtually 100% of the U.S. population having almost immediate access to paved roadways.”
“questions yet to be answered: (1) How do the existing links (roads) develop and degenerate? (2) How are new links added to the existing network? (3) How are new nodes added to the existing network?” “the Twin Cities transportation network which comprises nearly 8,000 nodes and more than 20,000 links, using network data collected since year 1978”
Specific questions on the rise and falls of roads:
- “Why do links expand and contract?
- Do networks self-organize into hierarchies?
- Are roads (routes) an emergent property of networks?
- What are the parameters to be calibrated in a microscopic network dynamics model?
- Is the model computationally feasible on a realistic transportation network?
- Is the model capable of replicating real-world network dynamics?”
“Longer, faster, and high-demand (traffic flow) links should be able to generate more revenues. If not maintained appropriately, link LOS [Level of Service] will decrease over time due to physical deterioration caused by the environment and traffic.”
“link expansion cost is positively correlated to lane-miles of expansion and road hierarchy (interstate, state highway, county highway, etc.), while negatively related to the distance from the nearest downtown” “most roads carry flows well below their capacity and a few roads operate at VC [volume capacity] ratios near or slightly higher than one. Practically, over a long period of time, no road can carry flows more than its capacity.”
“some important system properties, such as road hierarchies and self-organization in transportation networks, can be predicted through a microscopic evolutionary process, a demonstration that such a microscopic agent-based model of network dynamics can be feasibly applied to large-scale realistic transportation networks, and an enquiry into how this concept can be realized and produce useful modeling tools for planners.”