|
Comment on this article |
Email this Article
|
|
News :: Miscellaneous |
|
The Urban Network: A Radical Proposal |
Current rating: 0 |
by Peter Calthorpe
(No verified email address) |
28 May 2002
|
|
A pitch for a new kind of transportation network. |
 A pitch for a new kind of transportation network. |
Peter Calthorpe's abstract diagram shows how the Urban Network binds together a hierarchy of walkable centers with a range of new road types and intersection configurations. Transit routes and one-way couplets provide direct local and regional access to the centers.
The Urban Network: A Radical Proposal
California is expected to grow by 12 million people in the next 20 years. Many other states, while not growing as fast, are also experiencing major migrations to suburban areas as much as we may like development to focus on infill and redevelopment, such efforts will only solve part of the growth problem. Even Portland, Oregon, with its urban growth boundary and strong urban design policies, satisfies only 30 percent of its growth with infill and redevelopment.
There is a critical need for a new paradigm of growth on undeveloped sites - one that complements urban infill and revitalization. This paradigm would match a new circulation system with the new forms of land use now emerging through the New Urbanism and Smart Growth movements.
Our transportation network is still a suburban grid of arterials punctuated by freeways. On occasion, a transit line may overlay this auto-oriented framework, supporting transit-oriented development and the revitalization of some historic towns and cities. But short of that, New Urbanism and Smart Growth are forced to take place within a network designed for sprawl.
The old way
The old paradigm is simple: a grid of arterials spaced at one-mile increments with major retail located at the intersections and commercial strips lining its inhospitable but very visible edges. Overlaying the grid in rings and radials is the freeway system. The intersection of the grid and freeway is fertile ground for malls and office parks. This system is rational, coherent, and true to itself, even if increasingly dysfunctional.
To insist that we must build transit rather than freeways is simplistic, just as calling for infill development to the exclusion of new growth is unrealistic. This is not to say that transit and infill are trivial pursuits, but they are not and never will be the whole story.
We must develop a new circulation pattern that will accommodate cars as well as transit and will reinforce walkable places rather than isolating them. Bringing daily destinations closer to home is a fundamental aspect of urbanism, but it is not the complete solution to our access needs.
More than ever, regions define our lives. Our job opportunities, cultural interests, and social networks go beyond the borders of any single neighborhood or town. Even if we double the percentage of walkable trips in a neighborhood and triple transit ridership, there still will be massive growth in auto trips - not to mention an exploding quantity of truck miles. We need a system that accommodates all modes efficiently at the same time that it supports urbanism throughout the region.
New, diverse, and complex
The alternative transportation network proposed here is diverse and complex. It calls for a new hierarchy of arterials and boulevards that allow for through-traffic without always bypassing commercial centers - a road network that reinforces access to walkable neighborhoods and urban town centers without cutting them off from local pedestrian movement.
This new network must incorporate transit in a way that is affordable, appropriately placed, and integral to the system. It should reserve freeway capacity for long trips and provide alternate means for daily work commutes and shopping trips.
Our firm has developed such an urban network for Chicago Metropolis 2020, a private regional planning effort of the historic Commercial Club (the group responsible for the Burnham Plan of 1909). The plan for new growth areas around Chicago proposes three types of major roads to replace the standard arterial grid: transit boulevards, throughways, and arterials. The transit boulevards combine semi-local trips with some form of transit, the throughways are limited-access roads for long trips, and the arterials are similar to our existing grid.
These alternative street types would breed a different set of intersections: roundabouts and couplets of one-way streets. They would replace the slow, over-scaled intersections of our standard, signalized arterials. The roundabouts would expedite traffic on through streets, and the couplets would allow urban development adjacent to and even within a major intersection.
Beautiful boulevards
The transit boulevards are at the heart of this new network. They are multi-functional arterials designed to match the mixed-use urban development they support. Like traditional boulevards, they have a central area for through-traffic and transit. Small-scale access roads support local activities and a pedestrian environment at the edges. The boulevard is a place where cafes, small businesses, apartments, transit, parking, and through-traffic mingle in a simple and time-tested hierarchy.
The transit boulevards would be lined with higher density development and approximately every four miles would run through a "town center." At that point, the boulevard would split into two one-way streets set a block apart, creating an urban grid of pedestrian-scaled streets.
No street would have more than three travel lanes, allowing pedestrian continuity without reducing auto capacity. This one-way system would also eliminate left turn delays, actually decreasing travel time through the area.
The transit system running along the boulevards and through the town centers could be light rail, streetcars, or bus rapid transit. BRT is the most financially viable system for widespread use, particularly with the new super-efficient natural gas engines and advanced bus designs.
In contrast to the boulevards, throughways are single-use roads that provide for truck traffic and longer distance auto trips, much as our older highways do today. They are a viable alternative to congested freeways or stop-and-go arterials.
In our scheme, roundabouts would be placed at one-mile intervals, supplemented by infrequent right-in, right-out curb cuts. The roundabout is particularly important to this system, as its average intersection delay is up to half that of a typical signalized arterial intersection.
The throughway would support truck and auto-oriented land uses, such as low-density manufacturing, warehousing, and light industrial development. In some areas, these roads could be lined with open space areas and greenbelts. The tendency for strip development along such roads would be offset by the availability of development opportunities on the boulevards and local arterials, and in village and town centers.
Local arterials would have frequent intersections - crossing the throughways and boulevards at one-mile intervals - just as our existing suburban system does. At major intersections, an urban couplet could support a village center. In some cases, the local arterials could get a parkway treatment and be lined by large-lot houses backed by alleys, as in the historic neighborhoods of many American cities.
Multi-use, multi-scale
This urban network would replace the old system of functional street types, where streets serve a single function in a linear hierarchy of capacities. The new street types combine uses, capacities, and scales.
The transit boulevards combine the capacity of a major arterial with the intimacy of local frontage roads and the pedestrian orientation that comes with the transit system. Local arterials are multi-lane facilities that transition into a couplet of "main streets" at the village centers. This approach is fundamental to the more complex mixed land-use patterns of the New Urbanism. Streets, like land uses, can no longer afford to be single-purpose.
The urban network integrates new and old forms of urban development in appropriate and accessible locations. Walkable town and village centers are placed at the crossroads of the transit boulevards and local arterials. Residential neighborhoods are directly accessible to these centers by way of local connector streets as well as the arterials. Industrial, warehouse, and other auto-oriented uses are close to the throughways.
Each urban land-use type has the appropriate scale and type of access. The town center is both pedestrian friendly and accessible to the boulevard's through-traffic and transit line. The villages are directly accessible by foot, bus, car, or bicycle from their surrounding neighborhoods, while the couplet streets bring the auto access needed for retail. Auto- and truck-oriented uses can locate at the intersections of the throughways away from the transit and mixed-use centers.
Making retail work
Retail uses within the village and town centers need adequate access and visibility and an appropriate market area. For example, it now takes a minimum of 10,000 people or just under two square miles of mixed-density housing to support a full-service grocery store.
In the urban network, village centers anchored by such stores could be located at major arterial intersections without being cut off from surrounding development. Diagonal connector streets provide direct access for pedestrians, cyclists, and cars from the surrounding neighborhoods, while the couplet allows comfortable pedestrian movement through the center.
Surrounding the village are four neighborhoods, each defined by a quarter-mile walking radius and a mix of uses enhanced by access to the village center. An example of a village center organized this way is San Elijo, about 30 miles north of San Diego. There, a site originally planned around a standard arterial intersection was redesigned to place a village green at the intersection of four one-way streets.
In one quadrant, the grocery store anchors the primary retail area; in others, housing and civic buildings line the streets. Two main streets lead up to the green and mixed-use buildings will surround it. In two of the quadrants, a school and community park complete the center.
A town center contains much more retail along with higher density housing, major office development, and a more extensive street system. Issaquah Highlands, 17 miles east of Seattle, is an example.
This center is placed at the intersection of a major new arterial (projected to carry some 50,000 drivers a day to a new freeway interchange) and the entry to a new community of approximately 3,500 units of housing. The Microsoft Corporation has also acquired part of the town center for a second major campus of approximately three million square feet.
Splitting the arterials into one-way couplets allowed an urban grid to organize the site and provided for a more pedestrian- scaled environment. Under the standard configuration, the primary intersection had a 166-foot pedestrian crossing. In contrast, one of the couplet streets is just 28 feet wide; the other is 40 feet. Traffic engineers found that the auto travel time through the village center was actually reduced by 11 percent when compared to the conventional intersection pattern.
The spacing and configuration of the urban network can and should bend to environmental constraints and existing development. In retrofitting existing suburban areas, selected arterials could be converted into transit boulevards and some intersections reconfigured into paired one-way couplets at redeveloping retail centers.
A radical departure
The urban network is a radical departure from the norm. It posits a new hierarchy of streets, new intersection configurations, and a new set of land-use types. Yet it uses much of the same technology and many of the same institutions that built and are building our current suburban infrastructure.
Road builders would still lay down asphalt; auto makers would still produce cars, and buses as well; developers would continue to build communities. Further, all the advantages of the New Urbanism - its compact, land-saving density, its walkable mix of uses, and its integrated range of housing opportunities - would be supported and amplified by a circulation system that offers real choices in mobility and access.
Smart growth and New Urbanism have begun the work of redefining America's 21st century development paradigms. Now it is time to redefine the circulation armature that supports them. It is shortsighted to think that significant changes in land-use and regional structure can be realized without fundamentally reordering our circulation system. Only an integrated network of urban places and multi-use street systems can support the change we need for the next century of growth.
Peter Calthorpe is the principal of Calthorpe Associates in Berkeley, California. His most recent book, coauthored with William Fulton and published by Island Press, is The Regional City: Planning for the End of Sprawl.
|
See also:
http://www.planning.org/planning/nonmember/default1.htm
|
