Congress of the New Urbanism - New England
The Art and Science of Shared Streets, a.k.a. “Naked Streets”
By Norman W. Garrick, Connecticut Transportation Institute, Department of Civil and Environmental Engineering, University of Connecticut

Winthrop Street in Cambridge, Mass. is a sleepy utilitarian side street near Harvard Yard. In the near future, Winthrop Street will be a place of vibrant street life where all users–shoppers, diners, pedestrians, bikers, and vehicles–share the same space on equal footing.

The City of Cambridge plans to convert the street into what is known as a “shared street.” Curbs will be removed and sidewalks merged with the road through the use of a continuous textured surface.

 

The shared street concept, which is just beginning to take hold in the United States, is variously referred to as legible streets, self-explaining streets, or shared space in Holland where it originated. In the United Kingdom, some publications have even taken to using the term “naked streets” in reference to the fact that these streets are “stripped” of the signs and markings necessary for the operation of conventional streets. The thinking is that shared streets do not need signs and markings, because users are guided on their proper use by the physical design of the streets themselves.

The really salient feature of shared streets is not that they are ”naked” but that they are designed to be fully part of the public realm and not just a conduit for traffic. A vehicle is considered to be just another user that must negotiate space on an equal footing with shoppers, bikers, skaters, pedestrians and all. The idea is to make the street legible so users understand that it is a shared environment and behave accordingly.

Placemaking on the street

The best-known designer of shared streets is the Dutch engineer Hans Monderman who works in the northern Dutch province of Friesland. In 1998, Monderman converted an intersection know as de Brink from a conventional signal-controlled intersection to a simple brick-paved intersection. Ben Hamilton-Baille, a UK designer who has studied shared streets all over northern Europe, reports:

“While observing the workings of ‘de Brink’ in the center of the Friesland market town of Oosterwolde, I was intrigued to hear a traffic engineer and safety official remark, with satisfaction, how many ‘traffic violations’ were taking place each moment in the raised paved stage-like square that constitutes the new intersection. Trucks, bikes, cars and pedestrians intermingle with apparent chaos and disorder, using eye contact and careful observation to negotiate space. The guiding control of the state is absent: It relies entirely on informal conventions and legibility.”

n 2003, the “Laweiplein,” a major intersection in the city of Drachten that carries almost 20,000 cars a day, was converted from an unattractive, signal-controlled intersection to a shared street intersection. The Laweiplein is now a textured intersection where the sidewalk merges with the roadway. At the center is a roundabout delineated by a contrasting surface treatment, and at each of the intersection’s four corners are fountains that are lit at night. According to the city engineer, Koop Kerkstra, accident rates have fallen about 20 percent since the conversion and travel time for crossing the city has improved dramatically. This apparent success of the Laweiplein conversion suggests that shared streets are not just for low-volume local streets.

Controlled chaos = success

The consensus report from numerous conversions like these is that shared streets have significantly increased safety and have also improved traffic-flow efficiency. The primary explanation for these somewhat counterintuitive outcomes is that the shared street environment reduces vehicle speeds generally to less than 20 m.p.h.

From the point of view of traffic safety, research in the U.S. and Europe has long shown that 20 m.p.h. is an important threshold. Below 20 m.p.h., the chance of being severely injured in a traffic accident is relatively low. But 20 m.p.h. is also the threshold speed at which people are able to interact and maintain eye contact and pedestrians and bicyclists feel comfortable in a mixed-use environment.

The greater efficiency of traffic flow on shared streets is also attributed to the low speed environment. The theory is that intersections, which are usually the bottlenecks in built-up areas, function much more efficiently at lower speeds since traffic signals are not needed. This theory seems to be borne out in many instances where European cities institute area-wide 30 k.p.h. speed zones and find that the traffic moves much more smoothly.

The concept of shared streets has many of the same goals as traffic calming, but the approach to achieving those goals is quite different. Although traffic calming is typically based on adding devices to the roadway to slow or restrict traffic, it still relies on conventional traffic operational principles. In other words, the assumptions in traffic calming are 1.) that the pavement is for traffic and the sidewalk is for pedestrians, and 2.) that signs and markings are needed to regulate behavior. The concept of shared streets represents a break from these essentially conventional assumptions. Shared streets rely on social rather than regulatory controls to govern how all users behave. There is a growing body of data to show that in situations where there is a mix of different types of users, this design approach can be the most effective for safety and efficient traffic movement.

n the American context, the idea of shared streets (especially for busier urban streets) is probably as radical a concept as traffic calming seemed 40 years ago when it first appeared in Holland. The shared street concept challenges prevailing orthodoxy about how streets are designed and about traffic safety. The idea of regulating traffic and separating users in time or space is very ingrained in our design philosophy. The apparent success with shared streets designs in north Europe raises the question of whether the conventional approach to street design needs to be reconsidered both from the perspective of placemaking and of safety. The pending conversion of Winthrop Street in Cambridge might help to jumpstart this debate in New England.


Norman Garrick teaches transportation engineering at the University of Connecticut. He recently returned from a stint as a Fulbright Fellow in Kingston, Jamaica in the field of transportation and urban planning. He also serves as advisor to CNU on its ongoing project to develop guidelines for the context-sensitive design of urban streets.

Email: Norman.garrick@uconn.edu; web: www.engr.uconn.edu/~garrick

His other relevant articles include: