Redesigning road systems for global sustainability

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Denis White, and A. Ross Kiester. March 2008. Network topology matters: Network topology affects outcomes from community ecology neutral models Computers, Environment and Urban Systems. Volume 32, Issue 2,Pages 165-171

Design ideas

Redesigning surface-road systems --along with human ecology and the built environment-- for global sustainability of practices rather than growth

This is a draft document, in process (c) Douglas R. White under Creative Commons citation copyright.

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These are notes for regional development proposals that do not compete with but can join other proposal -- whether for better public transportation systems, downsizing and greater vehicle fuel and emission efficiency, more attention to ecological viability and a host of other proposals. Three-connected traffic conversions can enhance surface road systems, lower road construction costs, produce much more efficient traffic flow, with concomitant fuel-saving cost efficiencies, and reduce environmental degradation through pollution. The core ideas here can be tested through simulation and then through testing in contiguous traffic zones.

The problem of the built environment

The dynamical tendency of many urban economies today is to respond to needs in ways that meet demand rather than meeting the requirements of sustainability. Developers acquire a large appropriately zoned swatch of land and, if large enough, build a roughly rectangular grid of roads, including cross-roads with stoplights on major intersections. For the smaller subtracts they build for security and exclusivity, as if there were a coming armageddon. Streets in these ghettos of safety begin to branch like arteries, as if safety lie in having unique check-points along the entrances. Meanwhile, in the downtowns that have been abandoned by white or elite-flight, the grid pattern that once permitted cross-hatch traffic flow in residential areas becomes blocked as they are cut off by freeways. Authorities do not seem to mind when poor and ethnic neighborhoods are pinched off so there is a single street entrance where only residents or police have a motive to enter (e.g. downtown LA). (Citation/footnote: Mark Grannis).

Over time the suburban cross-hatch becomes frustratingly difficult to traverse with long suburban avenues strewn with stop lights on the thoroughfares and stop signs on the smaller streets (e.g. driving through the new NE Phoenix). With any distance to travel, the driver heads for a freeway as quickly as possible. As freeways get more crowded there is demand for more lanes and more freeways, even in parallel (e.g. the east Denver north-south freeways).

Cities like San Francisco show a contrasting pattern, where to go to work drivers first take a freeway and then fan out through other people's neighborhoods to reach their place of work. Studies of urban political attitudes show that driving experiences such as these increase tolerance and empathy for others, promoting democratic values. (Citation/footnote: Bren Social Ecology thesis).


Analytically, the modern transport economy is developing a surface-road crossing index (number of streets that meet at intersections, including endpoints with an index of 1) that alternates between 4 (the crossing), 3 (branchings) and 2 ending in 1 (the dead end of the capillaries feeding "gated" communities), with street indices of 3 (branching streets) largely used to branch within "closed" neighborhoods, with only one way in or out (e.g. Orange and San Diego counties, California, and many other areas of the world). The cross-streets for freeways require huge investment in overpasses and cloverleafs while the off-freeway cross-streets require stop lights that halt traffic at each intersection, sometimes allowing free-flow for right-turn on red (e.g. California). The 3 branchings of modern road systems are not systematically connected into a healthy alternative-route systems but into closed neighborhoods and dead ends. Traffic flows freely only into and out of "safe" dead-ended residential areas distinguished by a lack of stoplights and stop signs that can come to connote a closed neighborhood.

Previously, such regions as the European peninsula were branching (3-connected) road systems that allowed free flow, and the odd warrens and passageways in organic cities formed mostly 3-connected graphs, with relatively few crossings that required the kind of stoppage and alternation of modern urban stoplight systems.

A k-connected route system is one in which every pair of intersections has k completely alternative routes to reach every other. The Romans built the first subcontinental 4-connected road system to service multiple routes of travel of their armies, stationed strategically like the white stones on the go-board in a early stage of play, to anywhere in the empire.

The modern U.S. transport system that is emulated worldwide unmistakably replaces 3-connected road systems with ones that are 4-connected. Like the effects of American-engineering in building dams and levies and straightening the Mississippi, only to create more devastating floods, the 4-connected road system has highly adverse effects on global sustainability: huge construction costs for freeway overpasses and extra lanes to overcome congestion, fuel inefficiencies in off-freeway roads because of stoplights and stop signs, massive consequences for pollution and CO2 emissions, massive disregard for the ways that local and regional ecologies are disconnected and destroyed by roads and highways, and disregard for the ways that 4-connected secondary roads and overbuilt freeways disconnect and segregate neighborhoods to further stratify inequalities and social distances into a massive market-driven segregation system (Citation/footnote: Grannis).

Dynamics of congestion and decongestion

Dynamically, the 3-connected flow system is free-flow, cheap, and efficient, while the 4-flow system, in a planar geography, is flow-regulated and costly. One "solution" for 4-flow systems (especially suited to cold climates) is to build upward into a 3-dimensional space of high rises and crossovers between buildings at different heights (e.g. in downtown Minneapolis). Cars are left behind entirely, abandoned in underground garages. The 3-D 4-flow hi-rise system, however, is tremendously costly, and best fit only for great administrative and financial centers. Another 4-connected 3-D system is that of urban subway systems, now developing into multiple strata of slower subways with more stations at the first level, and much faster and more frequent subways with fewer stops at the second level (e.g. the Paris Meteor system with 100mph automated lines, reached by deep elevators or five-story escalators). Together with the 4-connected planar grid of modern transport systems outside the intensive urban areas, all these forms of architectural and transit design are, in the long run, unsustainable. They are too costly in fuel and emissions, in maintenance and replacement.

Three-connected transport systems for a planar geography, the archaic system, are both sustainable and efficient. They define the minimal planar intersection: the meeting of three streets or roads. If every intersection is three-cornered it is trivially easy and low cost to insure that every pair of intersections, no matter how distant, has at least three completely alternative routes that connect them. The lack of bottlenecks built into the archaic 3-connected road systems maay also have facilitated the emergence of "fair markets," in which there were independent routes to alternative buyers, and the same, for acquisition of goods, for alternative routes to sellers. No single middleman, stationed at one site, could monopolized right of passage, and thereby facilitative competitive price equilibra.

Three-connected transport systems are basically self-regulating because they are free-flow. There no necessity of stoppage in the right lane, only occasionally in the left lane as against oncoming traffic. A two-lane road needs only a widening for a left-turn at the approach to intersections, not a stoplight.

A contribution to Solutions

The idea of triconnected surface roads is a low-cost means of improving traffic flow and decreasing congestion by near-zero cost improvement of intersection structures so that vehicular flow is near continuous. This is possible when some streets are converted to pedestrian walkways and bicycle use only, so that each intersection becomes a tri-section (branching or side-branching)) of three streets only. Such intersections often exist in the form of Ys or Ts and usually require no traffic signals. Where traffic flow is heavy, a modified realignment of (usually existing but also new) traffic signals can use conventional red, yellow, and green to allow three states of flow: (1) right lane open (green), (2) merge with caution into left turn (yellow), and (3) stop (red), plus the use of yellow when green is about to change to red. Because all lanes are in constant use traffic flow is potentially continuous through all trisections, provided only that pedestrian and bicycle traffic is rerouted by: (a) walkways over (and occasional tunnels under) the continuous-flow streets and (b) enlargement of the contiguous pedestrian areas. The off-vehicle areas can be freely scaled up or down in size to fit the objectives of zoning and ecological benefits.

Over time, percentage of intersections that are converted to trisections may increase, and may do so until there is complete un-blockage of off-freeway traffic flow. This can easily put to an end an expensive and inefficient traffic systems that rely on stoplights and stop signs at 4-way crossings.

While freeways will continue to constitute their present free-flow structure, as non-freeway road systems increase in the percentage of trisections, these free-flow trisections can absorb more traffic and decongest the freeways -- provided that a certain number of new roads are built to trisection specifications so as to optimize the availability of multiple independent routes between any two points. The traffic-flow multiconnected optimum for routes in road systems has been proven to be three for intersection-independent or parallel routes between every source-destination pair (i.e., using "3-connected" in the formal sense as defined in graph and network theory -- see papers such as those by Harary and White, 2000, and the prize-winning paper by Moody and White, 2003). New simulations can demonstrate that it is the triconnected feature that prevents congestion. This feature can work efficiently because drivers, in choosing routes of least resistance, will transfer locally optimum behavior into optimum traffic decongestion globally without having to have global knowledge of their traffic system. The only new instrumentation required consists of equipping each car with a simple $2 dashboard-mounted compass that helps to navigate directionally toward a destination.

For long distances, of course, drivers will prefer freeways, but as the local trisection routes become locally optimized so that with less local stoppage, drivers will find that the off-freeway routes become quicker when they are close to their home or their destination. These local routes become more fuel conserving compared to the lower miles per gallon typical of 4-connected routings. Choice of continuous-flow routes with multiple branching are also more interesting because dynamic local optimization leads to a modicum of exploratory behavior, even when the same destination is sought habitually. There may be several dynamically optimal ways, for example, to drive to work. (Citation/footnote: Jon Kleinberg)

The simplest form of implementation of this proposal consists of three steps within a given area:

  1. Analyze the current road system structure, traffic, road width, population density, zoning, habitations, commercial properties and functions.
  2. Select an optimal designation of streets, one or more blocks long, to convert, at low cost, to pedestrian/bicycle use.
  3. Implement where needed the minimal necessary trisection traffic signals for newly converted trisections or to counterbalance increases in road use.

The triconnected road and stoplight system optimizes travel time, distance traveled, fuel, and benefits of alternate routings to the same destination, and the freeing up of nonvehicular spaces for alternate usages.

When used, the three traffic lights on a trisection alternate clockwise in British road systems and counterclockwise elsewhere, described here for right-side driving:

  1. Right green, across left yellow (merge).
  2. Right yellow (merge), across left red.
  3. Right green, across left red.

A given approach lane for a trisection switches from 1-2-3-1 counterclockwise and 1-3-2-1 clockwise. (Or, for the British system, substitute right for left, which gives an equivalent reversal). In right-side driving, every lane has one right turn choice to continue at regular velocity (1,3), or merge (2), while for the left turn signal 1 gives a merge option while 2-3 has a red stop. Only 1/3rd of the options are red, compared to 1/2 for California-law and 2/3rd for no right turn on red systems. (or, in the British system, again, substitute right for left).

This system suggests ways of redesigning communities and ecologies with maximal no-vehicle or uninterrupted open spaces for industry, agricultural, animal husbandry, and community spaces, with population concentration, parking, and consumer outlets strictly along low-flow roads, and a possibility for complete absence if desired, of dead-ends.

The benefits to contemporary human social, urban, suburban, peri-urban and rural organization are explained in the longer paper.

Historical reasons for the current cross-hatch or grid pattern road systems are examined, starting with the Roman highways.

The dynamics of Scalability and sustainability

The 3-connected transport system is optimized if every intersection is 3-connected. Forking branches or trisections that are 3-connected necessarily imply traffic rings, and the possibility of driving in a circle. In a 3-connected traffic system, every nonvehicular areas necessarily has a smallest traffic ring surrounding it. The area within this minimal right can be expanded and reshaped indefinitely.

Sustainable zoning requires that the space inside traffic rings be optimized, and that the potential planar geography inside traffic rings be off-limits for fuel-using vehicles and available to a variety of uses, including sustainable ecosystems.

... to be continued... the core idea being that massive changes can also be brought about with larger uninterrupted ecozones that might also benefit from ecozone triconnectedness ...

Road Systems for failed states, failing empires, displaced populations, and sustainable communities

I used this title in the first draft because the most developed economies already have their (costly) transport infrastructures in place, while most of the world, and the rural areas of the more developed world, are thus the most likely to benefit: this proposal can help economic recovery of regions devastated by war, instability, drought, famine, overpopulation, etcetera; it can help impoverished areas regain agricultural or economic viability; it can help large-scale political systems whose economies have crashed to recover economically, and it could conceivable provide a way of organizing new regional configurations that would provided ecological sustainability to refugee or relocated populations.


Stability domains group