In 2005, one very small act blew open the concept of urban redevelopment, wrenching it out of the hands of big-city planners and handing it to artists, activists, and, yes, architects. The principals at Rebar, a San Francisco design firm, converted a solitary parking space into a tiny park, complete with sod and a bench (while someone fed the meter), and launched what has become the worldwide PARK(ing) Day phenomenon. By the time Boston city officials issued a request for proposals for similar “parklets” around the city last fall, the do-it-yourself movement known as “tactical urbanism” had moved squarely into the mainstream.

Tactical urbanism refers to temporary, cheap, and usually grassroots interventions—including so-called guerrilla gardens, pop-up parks, food carts, and “open streets” projects—that are designed to improve city life on a block-by-block, street-by-street basis. In the post-Occupy Wall Street era, these efforts give concerned citizens and creative thinkers ways to reclaim built environments, encourage pedestrian traffic and street life, and promote economic investment without being bogged down in big politics and strangled budgets.

“The rapid ‘build, measure, learn’ process used by software engineers can also be applied to our neighborhoods and cities,” says Mike Lydon, founding principal of the Street Plans Collaborative, a research and urban planning firm, and a steering-committee member of the Next Generation of New Urbanists (Nextgen). “It turns the planning problem of endless studying on its head and heads right to building something, so that the results can be understood and communicated. It’s a creative, effective, and exciting way to respond to some of the more pressing problems our communities face, but at the scale most nonexperts can understand: the block, the lot, the building.”

These efforts also align with two major AIA initiatives now under way. First, AIA’s Repositioning initiative is shifting the organization to better reflect and serve its diverse membership, particularly the growing number of emerging professionals who are eager to do and not just discuss. AIA’s new Decade of Design initiative, in partnership with the Clinton Global Initiative and the Massachusetts Institute of Technology’s Center for Advanced Urbanism, is also aligned with the idea that tomorrow’s architects can benefit from focused research (in this case on public health) today.

Since that first San Francisco parklet, PARK(ing) Day public spaces have been created in nearly 150 cities worldwide, according to the Street Plans Collaborative, which has coauthored two tactical urbanism guidebooks with Nextgen. In Dallas, the Better Block program added a bike lane, plants, and sidewalk furniture to a moribund city block. In New York City, pavement-to-plaza projects have taken cars out of automobile lanes and put people there instead.

Injecting parkland into a small or underused urban area is not new. Situated on only one-tenth of an acre, Paley Park in Manhattan, with its 20-foot-tall waterfall backdrop, is widely considered one of the best urban parks in the world. Chestnut Park in Center City Philadelphia, which was recently restored and renamed for its designer, John F. Collins, is another well-known example. Tactical urbanism combines the ideals of these parks—exposure to beauty and nature, community connection, and efficient use of space—with less bureaucracy. The quick-turnaround, budget-conscious, easily adaptable techniques espoused by tactical urbanists are applicable to a variety of architecture projects, proponents say, and may be essential for recent graduates looking to compete in an ever-tighter job market.

“While the phrase and packaging of tactical urbanism might be new, the basic techniques have been used in various ways by the New Urbanists for decades,” Lydon says, citing as one example the use of small market stands to incubate businesses at Seaside, Fla., long before buildings were in place. “Our current work is an extension of these ideas, but also applying it with a slightly new lens that is also focused on the implementation and funding challenges facing today’s cities.”

In Boston, for example, city officials have now chosen four parklet locations around the city, each no larger than two end-to-end parking spaces. Two sites will be designed by Interboro Partners, a New York City interdisciplinary design firm, with the other two going to Boston-based Kyle Zick Landscape Architecture. Funding for this pilot program will come from the city, but local business partners will pay for maintenance. If the program catches on, city officials hope that funding for future parklets will bubble up from the community itself. “Parklets are part of the Boston Complete Streets Initiative, taking Mayor Thomas M. Menino’s directive that ‘The car is no longer king,’ ” says Rachel Szakmary, a city transportation planner. “The pilot program aims to show communities what is possible with all types of public spaces, in this case parking spaces.”

In San Antonio last year, three tactical urbanism projects following the Better Block model championed by community activists in Dallas have allowed city officials to see how redevelopment might work over the long term. One such project activated Alamo Plaza with music, food, additional seating, and a market, providing information that may guide future changes for the plaza for which funding has already been earmarked. “Proposed street closures and lane reductions in downtown areas are often controversial,” says Colleen Swain, a redevelopment officer for the city. “But if you allow people to experience the impact, rather than just see a plan or drawing on paper, then they feel more sure of their support or dissent.”

Similarly, the Street Plans Collaborative has documented a public art campaign in El Paso, Texas, that paved the way for a $90 million state investment in that city’s streetcar system. In Memphis, a weekend-long Better Block project led to $8 million in private investment along four blocks in that city. And a formerly temporary plaza in New York City has been reconstructed for permanent use.

“If any of the projects are to be sustained, they have to be adopted and championed in some way by institutions,” Lydon says. “So my goal is to use tactical urbanism to help transform what we call the ‘project delivery process’—that is, how things get done at the municipal level. A few governments are way out in front on this, but the majority is still stuck in a system that hasn’t evolved in 40 years.”

Even a major citywide project like the Atlanta BeltLine, where members of a large consortium of public and private partners are transforming old railroad beds into a 22-mile loop of transit, parks, trails, and public space, has a relationship to tactical urbanism. The concept began with a 1999 master’s thesis by Ryan Gravel, who is now a senior urban designer with Perkins+Will’s Atlanta office. Gravel, after studying abroad in Paris, began to value dense neighborhoods of street-level retail, parks, and transit that are defined by the totality of their arrondissements, or neighborhood districts, as much as they are defined by the character of individual blocks. He and others championed the BeltLine idea at the grassroots level until it eventually caught on with city officials and the mayor’s office.

Now, with more than $300 million in public dollars invested, plus another $40 million in private funding, implementation is under way to connect 45 in-town neighborhoods with trails and transit, and create 1,300 acres of park space, while also fostering economic development in formerly industrial areas and adding affordable housing.

“It’s like tactical urbanism on steroids,” Gravel says. “We built this amazing groundswell of support, even though, over the years, there have been challenges to the direction of the project—its vision, funding, ownership, and so on. If the public feels as if a bad decision has been made, they come out in force. They feel an ownership and an entitlement to adding new ideas to the overall vision.”

Recent grassroots ideas include building a swing on one section of the trail with a view of the skyline, installing guerilla public art projects, and creating a 22-mile “food forest” of locally grown produce along the route. Gravel, who says architects are uniquely skilled to work on this kind of creative, multilayered project, points to the in-studio work performed by Georgia Tech College of Architecture students on the BeltLine, under the professorship of David Green, AIA (a senior urban designer at Perkins+Will’s Atlanta office, who received AIA Atlanta’s Silver Medal in 2003 and Bronze Medal in 2008 for his contributions to community planning, city-wide). The students’ plans formed the basis of the Atlanta BeltLine Street Framework Plan that was adopted by the city.

“No city will build a bridge or a light-rail system with tactical urbanism alone,” Lydon says. “But creative and smart interventions can build the social and political capital needed to push such projects forward from the study and proposal stage. Tactical urbanism looks physical, but often the best results are social, in building more capacity and ties to longer-term change within neighborhoods.”

Learn more about urban placemaking through the AIA Regional and Urban Design Committee at aia.org/rudc.