CNU XVI – The Art and Science of Great Streets

One of the many good things about CNU XVI was that there was so much going on, so many good panels, that it was easy to find interesting topics about which to write. One of the bad things was that there was so much going on, so many good panels, that it was hard to find time to write about them.

It’s been a week since CNU XVI withdrew from Austin. The best of intentions for summarizing the panels I hadn’t gotten a chance to blog about yet were thwarted by a business trip from Chicago to New York on American Airlines. ‘Nuff said.

One of the more interesting sessions I attended was a 202 panel on enabling great streets. A lot goes into the making of a great street, and just as much goes into the making of a cruddy street: lane widths, turning radii, sidewalk widths, the presence of sidewalks at all, trees, onstreet parking, building placement and design and flower boxes are all key ingredients. How these are all put together in a “successful” way is, of course, subjective. The difference between a good street and a bad street can be as narrow as the different perspectives of a traffic engineer and an urban planner, and as wide as suburban arterial.

Ian Lockwood, senior transportation engineer at Glatting Jackson Kerchner Anglin Inc., said that over the years streets have become tools to move traffic, not things to be designed with aesthetics in mind. “Street improvement” has come to be synonymous with “street widening” and “efficient” now means “fast.”

Cities, he said, exist to maximize exchange—planned exchanges like trips to the store and unplanned exchanges like taking a walk and finding an art show at which you buy something. The quality of a city, Lockwood said, is the sum of the unplanned exchanges, and the key to those, and thus to good cities, is facilitating access. Planners and transportation engineers have always known this, but their pursuit of it changed in the post-World War II era. City transportation networks changed to accommodate motorists by reducing congestion the idea being that maximizing access meant making movement faster, which meant wider streets.

Lockwood called this shift “wrong-headed transportation planning,” and said the quest for greater automobile mobility spread cities out and created sprawling, homogeneous areas that don’t interact well. “Much of what we’ve been doing in transportation planning has been anti-city,” Lockwood said. The fact of the matter is that all great cities throughout history have been congested: Rome, Paris, New York. Cities that succeeded in reducing congestion in their cores have tended not to be successful. Take Detroit, for example. Or Newark.

It turns out that making streets wider not only doesn’t move traffic any more efficiently than a good interconnected network of more narrow streets, but arterials do a worse job moving cars and are less cost effective the wider they are. In fact, there is a law of diminishing returns per lane added, Lockwood said, since each additional lane can carry slightly less traffic than the previous lane. And walkability is enhanced greatly by more fine-grained street networks, as opposed to superblocks. Traffic just moves more efficiently, even at lower speeds, with more possible routes. An accident that closes three lanes of a typical six-lane suburban strip arterial is difficult to get around, whereas an accident that closes all four lanes of the intersection of two two-lane streets on a grid can be gotten around relatively easily.

Michael Freedman, principal at Freedman Tung & Bottomley, an urban design firm in San Francisco, said for the first time since its advent the strip is vulnerable. Development patterns have shifted once again, toward clustered retail developments and so-called lifestyle centers, located at major crossroads. The result has been disinvestment in the most visible portions of many cities and towns—their strips. This sounds bad, but it presents opportunities for redevelopment, provided communities come together to plan the transition of these aging strips to mixed-use, mixed density uses.

The new development plan is nodal, rather than linear, Freedman said. This will leave miles of land in between the nodes, and it’s there that strips can be turned into boulevards that include housing. The key is to find the “highest and best use” for entire corridors; that means retail at the major crossroad nodes but not in between.

Property owners and developers have been slow to realize this, as they are still keyed in on strip retail. Additionally, planners haven’t caught on completely either, and as a result residential development is often prohibited along these strip corridors, Freedman said. “Allowing housing uses land more efficiently, helps meet diversity of housing demand and meshes with transit goals,” Freedman said.

But the key to re-energizing and saving these aging strips is to create a pattern of centers and segments. The grand residential boulevard, as he described it, is a forgotten American tradition. They incorporate larger residential buildings fronting the street in the non-retail segments. These residential buildings accommodate a range of housing types and price points, from mansions to apartment buildings.

This grand boulevard arrangement is just the kind of integration of roadway and urban design that Eric Dumbaugh, assistant professor in the Department of Landscape Architecture and Urban Planning at Texas A&M University thinks is critical. What’s important in determining how a street looks and functions is the environment in which the roadway is placed. Proponents of highways and arterials like to point out that fatality rates per vehicle miles traveled have fallen in the highway era. However Americans drive more than residents of any other developed nation, so logically, “We haven’t really reduced the likelihood you’ll be killed on the roads, but you get to travel a whole lot more,” Dumbaugh said.

The logic goes that interstate highways see fewer crashes than other types of roads, so they must be safer. If they’re safer, we should apply the same design standards to all roadways, thus making all roadways safer. It’s simple, linear logic. And it’s totally wrong, Dumbaugh said.

Narrower streets with trees and parking on both sides encourage slower speeds, which although increased congestion yields more accidents, those accidents aren’t nearly as serious because of the lower speeds. High speeds are “entirely inappropriate” for urban areas for a number of reasons, not the least of which is stopping distances. A car traveling 40 miles per hour requires 300 feet to stop from the time the driver sees something blocking the road—like a person—until the time the vehicle stops. Portland, Ore., for instance, has 200-foot blocks downtown. At 60 miles per hour it takes 580 feet to stop.

Also, at speeds of 10 miles per hour, studies have shown that vehicles yield to pedestrians 100% of the time. Beyond 20 miles per hour, cars almost never yield to pedestrians, Dumbaugh said.

In Europe, street design is affected by place, in addition to desired movement, Dumbaugh said. In the United States, “we pay almost no attention to place, just the road function.”

Counterintuitively, perhaps, the presence of roadside objects, like trees, reduces the number of roadside crashes. “Drivers read the road, not the signs,” Dumbaugh said. “Seventy-five percent of drivers ignore posted speed limits.”

This reminded me that when the Port of Portland was building a new access road to Portland International Airport in the early 1990s, a big deal was made of the use of spacing between rows of trees, and the trees’ distance from the road, to affect drivers’ perception of their speed. As drivers approached the terminal, the trees were spaced closer together, and closer to the road, giving drivers the impression they were going faster. The goal was to make drivers feel they needed to reduce speed to match the driving conditions, rather than relying on “Speed 25 MPH” signs.

“We need to design roadways that clearly convey the risk associated with them,” Dumbaugh said. “If you’re putting up a lot of signs to warn of risk, the street is poorly designed.”

Brian Bochner, senior research engineer at the Texas Transportation Institute, gave an overview of the work the Congress for the New Urbanism has done with the Institute of Transportation Engineers coming up with a manual for designing contextual urban streets for walkable communities. More than 800 comments were received, and as a result parts of the manual are under consideration for revision. Revised recommended practices are expected to be approved later in 2008, he said.

Among the areas being worked on are addressing the tension between the document’s recommendations and local street standards, working out the difference between “target speed” and “design speed” (currently the target speed equals the design speed plus five miles per hour; the proposal is to make the target and design speeds equal), expanding the number of thoroughfare types, considering narrower traffic lane recommendations, providing mid-block signalization criteria, expanding the section on emergency vehicles and street design and including guidelines for small town main streets.

In all, Bochner said, there are about 100 changes to be made that go beyond mere editorial changes.


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