Highway Bridge vs Social Bridges

An early draft rendering of what the Casey area could look like with the at-grade solution.

By Anne Lusk, Ph.D.
The Casey Overpass has been discussed in the community based on moving traffic of all kinds, livability, aesthetics, personal preferences, and a variety of other motivations. If we can accept that both the bridge and at-grade options move traffic in similar ways, as traffic engineering models have shown us, personal preferences and how each option affects social behavior in the neighborhood might deserve a more careful analysis. The field of Environment and Behavior, i.e., environmental psychology, offers some explanations.
Humans, for evolutionary purposes, are information processors. To survive in what was originally a predatory landscape, humans need information and the ability to understand what they see (Kaplan and Kaplan 1983). The most preferred landscape offers “prospect and refuge” (Appleton 1975), meaning a place which allows a person to see far but also be hidden or protected. Thus, a preferred view is a landscape that includes smooth ground, such as grass, and spaced trees (Kaplan, Kaplan, and Ryan, 1998). The view then is open yet there are elements that enable a person to not be fully exposed as they would in a farm field or wide open parking lot.

Yet in this most preferred landscape with prospect and refuge, the person doesn’t always prefer full predictability. With predictability, they might become bored. Therefore, in addition to providing a landscape that is inviting, the ideal landscape should also include complexity and mystery (Kaplan and Kaplan 1983). The key is creating areas that are not boring, but also not stressful.

In an urban environment, one can be susceptible to overload as there is often too much information to process (Simmel 1950). Overload can come from too many people crowding in, but also from too much noise, pollution, dust, or the anxiety that comes from being uncomfortably close to passing traffic. In a 1972 study that looked at different types of streets, residents of wider streets with higher traffic were less likely to know their neighbors or recognize details of houses nearby, and they also complained more about noise, pollution, and resulting stress (Appleyard and Lintell, 1972). With too much noise, a person can become fatigued and less able to focus overall (Glass and Singer, 1973). Though cars can provide privacy, flexibility, and immediate transportation for the user, they can be an eyesore and also result in danger, bad health, noise, and parking issues (Alexander, 1977).

While a person is susceptible to information overload, in an urban environment they would not be bored, due to the complexity and mystery of their surroundings. Yet when they are suffering mental fatigue, a nice view of trees might rest their mind and restore directed attention to the tasks at hand (James, 1892, and Kaplan and Kaplan, 1983, and Kaplan, Kaplan, and Ryan 1998). Additionally, in an urban environment they would have the opportunity to have exchanges with other people. These exchanges could also be stress reducers and take place in locations described by Ray Oldenburg as a “third great good place,” i.e., coffee shops, beer halls, etc. between work and home (Oldenburg, 1989). Individuals might also meet these friends on the sidewalk and have an impromptu conversation (Whyte, 1980).

The built environment can also be designed to facilitate positive interaction between strangers. A “social bridge” is simply a place or situation where a social connection can be made (Lusk, dissertation 2002, Lusk, Federal Transit Administration 2002, Lusk, 2006). Five basic types of social bridges can be identified: assist, connect, observe, in absentia, and information.

In an assist social bridge, someone helps another, as in being taught how to rent a bicycle.

For a connect social bridge, the person would be connected to another by a third element, such as being at the same public bicycle pump to get air or getting a drink of water at the same drinking fountain. The connect social bridge was also characterized by William H. Whyte as triangulation (Whyte, 1980).

An observe social bridge is a somewhat vicariously witnessed positive interaction between others. An example would be having the view of a child bicycling with a parent on a cycle track.

An in absentia social bridge is sensing the powerful presence of the designer of a particular space. This can be felt through sculptural water that invites play or a beautifully designed park, such as Paley Park in New York City or the reflecting pool at the Christian Science Center.

The information social bridge is reading information provided by someone else. This can be in the form of maps of bicycle routes, historical placards or even street signs. Information bridges may also become connect social bridges, as when two people are reading a public map at the same time, or an assist social bridge, as one bicyclist directs another bicyclist who is lost by pointing out informational aids in the area.

The Casey Overpass replacement could be planned as an elevated highway with handsomely designed piers. Notable examples include garden colonnade pergolas that provide enclosure and yet allow filtered sunlight, as in Columbus Park in the North End. Architect Le Corbusier elevated houses on pilotis, including Villa Savoye. Frank Lloyd Wright elevated buildings sculpturally, as in Falling Water. These piers could serve the equivalent of trees and provide necessary refuge to enable the person to be partially hidden. Yet prospect, or a distant view, is also a human preference. This view would be available through the branches of trees or the top of the pergola. This long view, though, would not be possible through a building and yet people have felt privileged to stand in the spaces under Villa Savoye or Falling Water. Therefore, the elevated structure itself may not be the issue or even the opaqueness of the structure above, but, instead, what is actually happening overhead could be the element that causes stress.

If a highway is elevated, this means that cars are over people’s heads. Though the noise, pollution, and dust that are generated by an elevated roadway could also exist with an at-grade plan, perhaps the notion of having cars over one’s head is troubling. From an evolutionary perspective, an elevated highway may be similar to having lions or tigers over one’s head. The vulnerability may be too great. Though cars are less perceived overhead on the stone-faced Curley Bridge over Washington Street near the corner of Huntington Avenue on Route 9, the perception before the bridge and under the bridge is not the same prospect and refuge or restorative environment as on nearby Pond Avenue. Though the corridor on Pond Avenue is flanked by a park, similar to the Curley Bridge bridge area, no bridge exists with cars overhead. Similarly, the cars overhead on the Bowker Overpass on Commonwealth Avenue near Kenmore Square are dominant and seem to prohibit park use even though there are many remaining park elements under the bridge. Though complexity and mystery are preferred to not become bored, perhaps the shadows from the bridge, obstruction of the sky, noise and existence of cars overhead result more in stress than fascination.

Rather than elevate the highway bridge for through traffic, perhaps trees, grass, calmed traffic, cross walks with walk and bicycle signals, a coffee shop, and small stores near the transit station could be provided along with a variety of social bridges to foster a hub of social activity in the area of the Casey Overpass. Boston would then have taken away another elevated highway and, rather than just having roads on the ground, gained a neighborhood where the bridge once stood.


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Appleyard D, Lintell M. The environmental quality of city streets: The residents’ viewpoint. Journal of the American Institute of Planners 1972;38:84-101.
Glass D, Singer J. Experimental studies of uncontrollable and unpredictable noise. Representative Research in Social Psychology 1973;4:165-180.
James W. Psychology: the briefer course. New York: Collier Books 1962; 1892.
Kaplan S, Kaplan R. Cognition and Environment: Functioning in an Uncertain World. Ann Arbor: Ulrich’s; 1983.
Kaplan S, Kaplan R, Ryan R. With People in Mind: Design and Management of Everyday Nature. Washington, D.C.: Island Press; 1998
Lusk AC. Guidelines for Greenways: Determining the Distance to, Features of, and Human Needs Met by Destinations on Multi-Use Corridors [Ph.D. Dissertation]. Ann Arbor: University of Michigan; 2002.
Lusk A. Bus and Bus Stop Designs Related to Perceptions of Crime. Washington, D.C.: Ann Arbor Transportation Authority; Great Lakes Center for Truck and Transit Research;  Taubman College of Architecture and Urban Planning – Environment and Behavior – University of Michigan.    U.S. Department of Transportation; Federal Transit Administration, Office of Research, Demonstration and Innovation; 2001 July. Report No.: FTA MI-26-7004-2001.1.
Lusk A. Promoting Health and Fitness through Urban Design. In: Platt RH, editor. The Humane Metropolis: People and Nature in the 21st-Century City. Amherst & Boston: University of Massachusetts Press; 2006.
Oldenburg R. The Great Good Place. New York: Paragon House; 1989.
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Whyte WH. The Social Life of Small Urban Spaces. Washington, D.C.: The Conservation Foundation; 1980


  1. Jessica Mink on March 8, 2012 at 11:34 am

    In the case of the Casey Overpass, I have found that most of the proponents of the at-grade solution *never* actually use this intersection. One could argue that the reason is that it frightens them, but the more likely reason is that they simply have no reason to. The use the #39 bus or Green Street or Stony Brook station instead of Forest Hills station because those forms of transportation are closer to where they live. The group which has been trying to avoid widening New Washington St. to six lanes and increase traffic on it consists mostly of people who either live or work very near Forest Hills or pass through the intersection several times a day. We have been *very* frustrated by MassDOT’s fairly transparent preference for not rebuilding the overpass and also upset by the strong feelings against a bridge by people who are simply against a bridge, not apparently caring how hard it will be to cross the resulting intersection by foot, bike, or car. This six-lane rad will *not* reconnect a neighborhood, but disrupt it!

  2. William Furr on March 14, 2012 at 1:13 pm

    Nice use of anecdotal evidence as opposed to scholarly citations, Jessica. I am against a bridge and I pass through that intersection every day.

    Mass DOT prefers not rebuilding a bridge because the bridge is not better! It’s quite clear in the traffic modeling and analysis based on livability criteria. A six-lane road is certainly not ideal, but it’s far better than a bridge with on and off ramps. Pair the six-lane road with $15 **million** dollars of pedestrian, bicycle, and transit improvements AND greater potential in the future for reconfiguring the streets and surrounding space, and now you have a neighborhood instead of a highway interchange.

    In any case, it’s moot. Time to move on.

    Help me advocate for separate cycle tracks and prioritization of pedestrians, cyclists, and transit users and accommodation of the cars, not the other way around.

  3. Robert Fine on March 26, 2012 at 6:52 am

    I wish that all people affiliated with Harvard would spend their time pressing their own administration to move forward on the Science Center in Allston than offering their analysis on what’s happening in Jamacia Plain (unless of course they live near there). The North Allston area they have suspended construction on is a disgrace and is far more of an eyesore and than the aging Casey Overpass.
    I do like the concept of Social Bridges though! I never realized it before but I suppose my Dog is a Social Bridge since he enables me to meet my neighbors, maybe I’ll change his name to Zakim.

  4. Kiesha Guarracino on November 11, 2012 at 8:09 pm

    You and your staff (if you have one) are awesome! Thank you so much for the versatality in subjects. I’ve been subscribed for about 5 or 6 years now and now that there is Facebook! Wow! Thanks again. Blessings from California…

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