I was in Harvard Square one evening last fall when I light rain began falling. A girl dashed out of a convenience store doorway, hurrying for an unknown reason. Turning the corner she abruptly slipped and fell on the brick sidewalk. No quicker than she had fallen she jumped up, unhurt, to continue on her way. Yesterday in Downtown Crossing, a man using crutches slipped on wet and snowy brick just as I left my office. These incident are repeated thousands of times in Boston and around the nation, at times resulting in injury. Sidewalk slips are commonplace, yet illustrates the complex ethics of contemporary urban planning. The material that contributed to these falls, brick, has many well-known flaws including a low friction coefficient when wet. However in the convoluted calculus of sidewalk materials, the grip of material surface inevitably falls behind a host of other factors.

From the point of view of pedestrians, there’s not much to like about brick sidewalks. When wet they’re often slippery. Bricks easily become uneven or loose due to tree roots or uneven soil, complicating shoveling and leading to tripping. The uneven surface can be treacherous for bikers, strollers, or the impaired. Some even point out they can easily become projectiles in the hands of miscreants. Yet brick remains a common material throughout many cities. Boston’s tourist meccas, Faneuil Hall’s plazas, Downtown Crossing’s streets, and even the Freedom Trail itself are made from brick. In Washington, D.C., miles of new brick sidewalks have been installed in the past few years in some of the city’s busiest pedestrian corridors.

Not everyone agrees with the brick critics. Commenting on a neighborhood newspaper’s story, titled “bricks bring worries for some pedestrians,” the Washington City Paper‘s sharp-tongued editor Erik Wemple rejects the complaints of a scooter-bound disability rights advocate quoted in the story and declares, “Brick sidewalks are one of the greatest ever streetscape accomplishments of the District government.” He neglects to mention that for recent streetscape projects, city contractors lay bricks on top of a solid pored slab of concrete, essentially building two complete sidewalk surfaces on top of each other. This approach combines the stability of cement with the aesthetics of brick, perhaps by sacrificing cost. (Government waste is another City Paper favorite topic)

Arguing they save money, trees, help recycle automobile tires, and create a superior walking surface, one California company is marketing rubber sidewalks. (Illustrated above) Despite a flurry of interest in 2006 (including here in Boston), the concept doesn’t have seemed to catch on in a big way, with local installations limited to a smattering across the country. The company’s own comparison chart may suggest the reason: it costs over $19 a square foot, versus an estimated $15 for concrete or $5-$8 for asphalt. I suspect other reasons are to blame, including the slow pace of change by municipal officials that make material decisions. The perceived pertinence and durability of cement may trump the actual durability, to say nothing about the demand for bricks based solely on aesthetics. Just the term “rubber sidewalk” conjures up images of a tactile, bouncy surface inappropriate for a city street.

The Federal Highway Administration’s report on designing sidewalks and trails orders sidewalk surfaces should be slip resistant under dry conditions (illustrated by this diagram), concluding “most asphalt and concrete surfaces are fairly slip resistant.” A Canadian report (Federation of Canadian Municipalities, Sidewalk Design, Construction and Maintenance) advises municipalities:

In choosing the material for the sidewalk, consideration should also be given to materials that are non-slip and provide adequate drainage, as well as the requirements of users with strollers, inline skates and also the visually and mobility impaired.

The report doesn’t even mention brick, but includes this list of factors for material selection conspicuously omitting safety: life cycle cost (initial construction cost, maintenance cost), durability, service life, location, maintenance, color (concrete reflects more light), vandalism during curing (pre-cast pavers), runoff potential. Just about the only people I can find considering safety in a serious way is the website of a odd advocacy group based in Arlington, Virginia, who complain about the rough surfaces create by bricks, cobblestones, course aggregate, and other materials.

Slippery sidewalks have become a problem, sparking legal action in that very pedestrian city, New York. A 1981 story in the New York Times describes how “new” materials like travertine and terazzo were slippery and resulting in lawsuits from people who fell on them breaking bones and suffering other serious injuries. According to the story, lawyers “in negligence suits, such cases are on the rise as a result of the wider use of a variety of materials for sidewalks to obtain a more esthetic effect than concrete provides.” A “noted” negligence attorney quoted in the story describes how he usually sues the property owner, not the architect or city, for putting down a defective sidewalk, noting adding the city to lawsuits “complicates” them.

With so many complex factors influencing sidewalk materials floating around, we should add the factor of local control. During a walking tour of Washington, D.C.’s H Street neighborhood last year, our guide told us how the most important factor in sidewalk materials was how well it resisted unsightly stains caused by chewing gum. They opted for a cement aggregate, rather than a plain concrete face or brick. Like in many issues, given the uncertain ethical calculus for sidewalks (how should professionals weigh aesthetics, cost, safety, vandalism potential, tree health effects, etc?) city planners defer to the preferences of active local residents. And if those who prefer a higher friction coefficient on wet days aren’t present, so be it.

In Harvard Square near where I witnessed the fall this fall, another person fell in October and was transported to the hospital for stitches. Maryan Amaral, a wheelchair user who frequents the area and witnessed the accident, convinced the City of Cambridge to re-build the sidewalk and crosswalk on the street after collecting 125 signatures on a petition. Happy with the new crosswalk ramps, she’s concerned about the material the city chose, however, pointing out that brick sidewalks often come loose. A lone comment on the online version of the news article about the case begs, “Please, let’s get rid of the brick sidewalks. I know some like their historic charm, but they’re just terrible in the ice and snow, both because they’re difficult to clear and because they tend ice over more readily than concrete. They’re also terrible for the handicapped.” Maybe the next petition will take up the issue.

> Federal Highway Administration: Designing Sidewalks and Trails for Access
> Cambridge Chronicle: Complaint Triggers Appian Way Rehab
> Book: Slip and Fall Prevention

Thanks to my friend Katie Mencarini with the Toole Design Group for help doing research for this post. Photos from Flickr users Lodigs and Supergiball