Design manual for urban thoroughfares ready for release

ROBERT STEUTEVILLE

What has been described as a seminal publication, one that represents a paradigmatic shift in thoroughfare design in the US, is nearing completion. The Institute of Transportation Engineers (ITE) is hoping in March to publish a draft of Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities, which will then be subjected to professional review. The forthcoming document has so far received both praise and criticism — several prominent new urbanist street designers say it calls for streets that are too wide, with speeds that are unpleasant and potentially dangerous for pedestrians.

ITE’s proposed recommended practice is the result of a five-year collaboration with the Congress for the New Urbanism. The Federal Highway Administration and the Environmental Protection Agency funded the book. After publication, which may occur in time for a March 19 ITE gathering in San Antonio, a comment period will ensue, ending Dec. 31, followed by the drafting of a revised manual that will be submitted for final ITE approval.

In dealing with major urban thoroughfares — including arterial and collector streets — the book covers a particularly challenging problem for new urbanists. Although taming streets is not always easy, there are hundreds of examples of recent projects containing narrow and walkable local streets. These projects tend to be islands of urbanism bounded by wide, relatively high-speed thoroughfares. In some instances, large new urban projects are plagued by internal collectors and arterials that discourage pedestrian activity. Plans that deal with sizable areas in the suburbs, and even urban infill projects, tend to falter when it comes to taming major thoroughfares.

Many of those who helped put the document together told New Urban News that it represents a radical departure in many respects from existing street manuals like the so-called Green Book published by the American Association of State Highway and Transportation Officials. The Green Book focuses on three factors — capacity, speed, and topography — in the design of thoroughfares, according to Brian Bochner, a senior research engineer at the Texas Transportation Institute who was a member of the project management team. The new manual views a host of other considerations — including pedestrians, transit, and placement of adjacent buildings and businesses — as central to the design of urban thoroughfares. “It goes into very great detail on roadside design and building design, aspects of thoroughfare design that we have no guidelines for anywhere,” says Norman Garrick, an associate professor of civil and environmental engineering at the University of Connecticut, a member of the review committee, and cochair of the CNU transportation task force.

Very importantly, the concept of the Transect — called context zones in this book — is used throughout the manual. The context zone must be identified prior to designing a “context-sensitive” thoroughfare, according to the book. “It gives designers a way of dealing with these concepts through the context zones — which we didn’t have before; all we had was [the designation] urban and rural,” Garrick says.

The book represents a leap forward in context-sensitive design thinking, says Ellen Greenberg, a principal with Freedman Tung & Bottomley, who led the effort on behalf of CNU along with Heather Smith, planning coordinator. Context-sensitive design previously recognized the importance of historic structures, but not typical buildings and public spaces, Greenberg says. “It’s not just about ‘don’t blow up a historic bridge,’ it’s about responding to the typical elements that make up the urban fabric,” she says.

The book offers substantially new thinking on street networks. It recommends high levels of network connectivity with small block sizes — preferably 200 to 300 feet in urban cores and 200 to 400 feet in less dense urban areas. The approach to curb return radii is also substantially different from conventional practice, notes transportation engineer Walter Kulash of Glatting Jackson, who reviewed only that section in advance. The book acknowledges the legitimacy of occasional encroachment of large vehicles in the opposing lane, a reform that he says is “badly needed.”

AREAS OF CONTENTION

For all of the positive aspects of this manual from a new urbanist perspective, significant areas of contention remain — in design speed and lane width, both of which are critical to walkable streets. The book contains no thoroughfares with design speeds of less than 30 miles per hour, notes Rick Hall of Hall Planning & Engineering, the only member of the review committee to vote against the draft. Hall, Rick Chellman of TND Engineering, and Peter Swift of Swift and Associates, three of the best-known street design engineers involved in New Urbanism, were all critical of the book’s approach to setting the design speed five miles per hour higher than the “target speed.” This thinking, which Chellman says originates in highway design, is inappropriate for urban thoroughfares, he contends. “When streets are designed for faster-moving vehicles, then we encourage faster operating speeds,” Swift told New Urban News. “The justification for providing a ‘factor of safety’ for speeding vehicles is bogus.” Swift, who is currently working in Kurdish Iraq, reviewed an advance draft of the manual.

Related to design speed is lane width, and on this issue the document offers no significant change, but a shift in emphasis. Lanes of 10 to 12 feet wide are recommended for collectors and arterials. These are the same dimensions given in the Green Book, says Bochner, although the Green Book shows a clear preference for the higher end of the range, and the ITE-CNU manual does not. New urbanists like Swift and Hall continue to push for 9-foot lanes, but this dimension is not included in the text. Even the Green Book allows 9-foot lanes in unusual circumstances, Bochner notes.

Swift notes further that gutters are excluded from lane widths in the new document. “This is a fatal flaw in cross-section design,” he says. Gutter pans are up to 2 feet wide, which makes a 10-foot lane seem like 12 feet, he says. “The controlling factor in reducing vehicle speeds is the curb face width because a curb is seen to be a barrier, not a gutter pan,” he says. Garrick, who voted in favor of the draft, acknowledges that street widths are a serious problem. Greenberg, a member of the project management team, notes that when all of the recommended and optional elements are put together “you end up with a really big street, which didn’t get a lot of attention,” she says.

Most of those involved with the project that New Urban News interviewed acknowledged flaws in the document. Bochner says the recommended practice is “80 to 85 percent there.” Greenberg believes the comment period represents a genuine opportunity to make constructive improvements in the recommended practice. She hopes that a significant number of comments will be made, because ITE is highly responsive to practical comments, she says, and a large number of comments show a high level of interest in the recommended practice, which tends to keep the process moving forward.

A reviewer need not be a transportation planner or engineer to be taken seriously, Greenberg says, noting that the technical sophistication of the comment is more important than the credentials of the source. Greenberg also urges new urbanists to “comment on what you like about it, not just what’s wrong with it.” To submit comments, go to www.ite.org.

COMPROMISES

Some of the difficulties with the document, Hall says, stem from what he calls a significant compromise made early in the development process — retaining the use of the terms “arterial” and “collector” rather than the new urbanist street lexicon of “boulevard,” “avenue,” “main street,” and “street.” The document tries to reconcile these two descriptive systems, with mixed results. Although arterials and collectors are defined in the manual, it is not entirely clear when a street that new urbanists would call a “boulevard” or a “main street” becomes a “major urban thoroughfare,” for example, and would thus be subject to these standards. The question is not without consequence, because the prevailing view among new urbanists is that main streets should not be designed for speeds higher than 25 miles per hour, while standards in this book start at 30 miles per hour.

Another compromise was the inclusion of high-speed thoroughfares in what the book calls “vehicle mobility priority areas.” New urbanists felt they should not be in the book at all, expressing the view that there are plenty of good manuals for high-speed thoroughfares, but the proposed manual is for walkable communities. Partly because of the collaborative process and writing by committee, Greenberg says the document is not as “sharply focused” as she would like.

Flawed or not, most agree that the book represents significant progress. “Just the fact that ITE is lending its name to it and supporting it is a big step forward,” says Kulash, who was eagerly awaiting the chance to read the proposed practice in its entirety. “Can you imagine something like this happening five years ago? The answer is no.”