ITE prepares to tentatively endorse narrow streets

Report recommends shared street lanes, but lacks hard numbers

Practitioners of New Urbanism have been waiting years for an officially sanctioned, authoritative document endorsing the kind of narrow streets appropriate for neotraditional projects.

The Traditional Neighborhood Development (TND) Street Design Guidelines, released for comment by the Institute for Transportation Engineers (ITE), offers no recommended street widths -- not even recommended examples or ranges of potential widths -- that new urbanists can use to justify streets that are, for example, 24 feet wide with parking on both sides.

That aside, the TND Street Design Guidelines contain a lot of important information and, even more significantly, endorse shared lanes of traffic, also known as “queuing” or “yield movement.” That concept, critical to designing streets for TNDs, represents a major reversal of traffic engineering orthodoxy of the last half century.

According to conventional modern traffic engineering philosophy, street widths are calculated by adding all travel and parking lanes together. Therefore, the width of a two- way residential street with parking on both lanes is determined as follows: two 10-foot travel lanes plus two 7.5 foot parking lanes equals the typical 35 foot distance curb to curb. Such a street generates traffic in excess of 30 miles per hour (mph). That’s the wrong way to calculate street widths, according to the report. “

A principle that is central to the design and sizing of streets in a TND is that where streets are not striped for separate lanes of travel, designers must not automatically think of separate lanes of traffic or parking in an additive sense (with respect to lane dimensions),” the report states. “An example of this concept can often be found on relatively narrow residential streets, either at low densities or when rear alley access is provided to the buildings. On these streets, with intermittent on-street parking, the street’s width may occasionally require one driver to slow down or pull over to let an oncoming vehicle pass before proceeding, particularly if one of the vehicles is a truck or other large vehicle.”

The report goes on to say that “this sort of occasional vehicular stopping should be considered normal along TND streets (emphasis added).” Where is this concept of shared street widths or queuing appropriate? “Especially for Types I, II and III streets (relatively quiet streets, with a maximum of 2,500 automobiles/day), as well as streets where significant nonmotorist oriented retail is located,” according to the report. Frank Spielberg, chairman of the committee that created the guidelines, adds that the majority of streets in a TND would be types I, II and III. The exceptions likely include major commercial streets and boulevards. According to TND traffic expert Walter Kulash, yield movement can be achieved with a maximum width of 28 feet (two way traffic, parking on both sides). The Operating System of the New Urbanism, Andres Duany’s work in progress, recommends 24-foot streets (two way traffic, parking on both sides). Design speed and safety The ITE report states that the “the desired upper limit of actual motor vehicle speeds on TND streets is approximately 20 mph.” This speed allows the creation of the “safest streets for a TND or other pedestrian enhanced neighborhood. Because a vehicle’s kinetic energy, sound, and the difficulty of seeing the driver all increase dramatically with vehicular speed, speeds at or below 20 mph are also the speeds that are generally the most aesthetically pleasing for pedestrians and bicyclists.” The argument is bolstered by research that shows dramatic increases in serious injury and death in cases when pedestrians are hit by cars traveling in excess of 20 mph. Research by Rudolph Limpert is cited, concluding that “the possibility of a pedestrian receiving fatal injuries is 3.5 percent at 15 mph, 37 percent at 31 mph and 83 percent at 44 mph.” Modifying the grid For those familiar with The New Urbanism, it should come as no surprise that the report argues for an interconnected street network. However, the report clearly advocates a modified, rather than pure, grid. “Most TND streets are designed to minimize through traffic. This concept is often accomplished by using three-leg or “tee” intersections, street widths, occasionally one-way routings, and general street network design.” The goals of creating an interconnected street network and the minimization of through traffic seem contradictory -- but the TND designer must keep them in balance, ITE says. “One of the challenges of TND design is to allow the diffusive flow of traffic without creating short-cuts that encourage cut-through traffic.” Other street elements The report has much to say about elements of a streetscape that are often taken for granted -- e.g. sidewalks, street plantings and parking. Relatively generous sidewalks (at least five feet in width, as opposed to the usual four feet) and street plantings (planting strips six or more feet in width with trees) are recommended. “In four feet of walkway, two pedestrians walking in opposite directions can pass by each other with relative comfort, but two pedestrians cannot walk comfortable together (unless in each other’s arms),” it states. According to Spielberg, the generous sidewalks and plantings should not add to the overall cost of the street if the curb-to-curb distance is reduced. Explaining the lack of numbers The lack of specificity on street widths in the report was partly due to not enough time and resources, Spielberg explains. At least four years was spent writing and revising the guidelines, largely work done by Chester E. (Rick) Chellman, of White Mountain Survey, the principal author. “Had we tried to come up with specific numbers, we probably would have spent another four years arguing whether the street should be 23, 24 or 25 feet and not get anything out,” Spielberg explains. “We felt it was important to get something out on record that ITE is accepting of narrower streets, rather than arguing over how much narrower.” Furthermore, many committee members believe that one of the problems with current street standards is that they are “too proscriptive,” and don’t give enough latitude to the designer within the context of the overall plan, he says. Kulash, who was not a member of the committee drafting the guidelines, says that the report “is good for setting the direction and outlining the basic principles, but there are a lot of people looking for clear, simple numbers (on street widths). Those people won’t find what they are looking for.” However, reform is taking place on the municipal level, Kulash adds. “Local governments are approving narrower street designs by the dozen -- the professional organizations eventually will follow their lead.” To obtain a copy of the proposed Traditional Neighborhood Development Street Design Guidelines, contact the ITE: (202) 554-8050. The official comment period was extended to September 15, 1997, but comments may be accepted later. Final guidelines may be approved in January.