CAMBRIDGE, Mass. — For decades, a stretch of Memorial Drive here that runs along the Charles River has been closed to automobiles on Sundays for the warmer half of the year. In the absence of cars on a four-lane thoroughfare beside the water, all kinds of other street uses blossom: skateboards, bicycles, hoverboards, strollers, wheelchairs and walkers, people on feet and on wheels now moving slowly enough to witness the late spring goslings, the ever-present sea gulls or the rarer magic and grace of a heron feeding along the water’s edge. A towering line of stately, centenarian sycamores forms an unbroken canopy over several blocks.

This section of Memorial Drive is formally called “Riverbend Park” during its weekend closures, but it’s not a park in any physical, structural sense. It’s an open public space transformed into a park without any construction. State park employees arrive in trucks in the morning and again in the evening at junctures in the road, placing gates, cones, and signs that cut off traffic. By dusk, the gates disappear, and traffic returns. That’s it — a park that is “found” from what’s already there.

It happens in cities everywhere: design, or redesign, created by time. A weekend clock turns an open street into something else entirely — a time structure organized outside commuter efficiency or traffic flows. Urban planners sometimes call it “temporal zoning.”

In 2020 and 2021, in response to the need for outdoor recreation during the pandemic, the city of Cambridge added Saturday hours for Riverbend Park, doubling its recreational time. Two luxurious weekend days of an open street from April to November — a provisional state of the built environment, like hundreds of other pandemic-led pilot projects happening right now all over the world. Each of these urban innovations carries with it a question: Can this last? Should it?

As cities across the world open up, urban planners and architects — and the rest of us — are looking around, asking whether our streets and buildings will be, or should be, the same again. But whatever we decide, there’s one transformational tool for building the cities that’s right in front of us, calling for more sustained attention: the design of time. We can creatively reorganize our collective hours and days in ways that help more people enjoy our cities and institutions. Time might be our most valuable resource for building the environments we want.

Covid-19 brought about temporal designs of other kinds. Starting in spring 2020, cities from New York to Bethesda to Berkeley repurposed city streets for outdoor dining, allocated by hours of the day. Retail shops everywhere, from grocery stores to booksellers, dedicated “seniors-only” browsing hours to vulnerable customers. In London and other cities, crosswalk signals were extended in length, an accommodation for more pedestrians in a season of fewer transit rides. It took responsiveness under duress to refashion the streets and spaces of our lives. Some of that ingenuity used the invisible tool of the clock.

Riverbend Park in Cambridge and “found” parks like it are created from a declaration, or more precisely a reclamation, of time — without expensive construction or risky permanent changes. Our collective clock got reset in a crisis, showing us that our time might be spent differently. The pandemic may ultimately force us — or beckon with an invitation — to see the clock as a resource for the cities we want, one that’s always been right in front of us: an undersung and powerful utility on a designer’s tool belt.

Designing with time may seem like an abstract concept best left to civic planners and public officials, but it’s important to remember: Sometimes the designer is an ordinary citizen.

In 1974, Isabella Halsted lived on Memorial Drive in Cambridge, one of the “river roads” that connects downtown Boston to its outskirts. She saw the Charles River every day — blocked by the constant traffic. This river — the city’s jewel, girded by plenty of green space — is mostly experienced at the pace of a car, rushed and blurry. But Ms. Halsted, who had grown up in nature, wanted more of that waterfront and green space to be present in its quieter, slower form — for herself and for her whole city. So she sent out several hundred postcards asking her fellow city residents whether they might support a novel idea: to close one section of the street to traffic on Sundays.

She formed the Riverbend Park Trust the following year. The group got permission to try out the idea, and held an enormous picnic in the street to celebrate. A small group of volunteers worked to raise the money to cover the basic expenses of Riverbend in its early form: portable toilets and park rangers. The Trust lobbied the Metropolitan District Commission to approve Riverbend one year at a time, before the idea’s momentum was sufficient to make it permanent. Since 1985, it has been managed by the Massachusetts Department of Conservation and Recreation.

Time has long been a way to rethink the design of cities and spaces. There are lightweight versions — a baseball diamond that is designated as an off-leash dog park in early morning hours, for example. Some shopping malls open their doors before regular retail hours, allowing people to walk their corridors for exercise — a safe and smooth passage especially appealing to older adults.

Time can also be a transformative tool for redesigning spaces with more ambitious goals in mind, making the built world more accessible and equitable. Many museums have made adjustments to their modes of physical access — ramps and elevators and audio tour apps — but meaningful accessibility might also call for a creative shift in time. At the Smithsonian Institution museums in Washington, D.C., for example, a time-based program called Morning at the Museum makes exhibits much more friendly to patrons with disabilities, especially those with intellectual or developmental disabilities.

Ordinarily an exhibition is designed to be visually and aurally dynamic, with plenty of interactive sounds and lights. But when community research made it clear that some people with autism spectrum conditions found these features difficult to be around, staff members realized they were excluding a constituency that would enjoy the museum more without these intense sensory experiences. Instead of redesigning the architecture or software to make a permanent change, Access Smithsonian, the institution’s office for accessibility, designed a clock-bound structure to accommodate these sensory needs. On dedicated weekend days, one of the museums opens early for visitors with disabilities of any kind — an open door to whoever needs it, says Ashley Grady, the senior program specialist who oversees the program. The Morning at the Museum staff makes adjustments to some exhibit features — turning down the sound or dimming the lights and offering targeted pre-visit prep materials. For a set number of hours, a museum offers a particular welcome to an overlooked population.

In Mexico City, Gabriella Gomez-Mont, who ran the wide-ranging and experimental Laboratory for the City between 2013 and 2018, used time structures to recover play space for children. The city was home to more than two million children as of 2015, and its green spaces and parks are unevenly distributed. Ms. Gomez-Mont’s group worked with residents in a pilot neighborhood to recapture play space for kids where no built structure was available. They tried a time experiment once a week: one street closed to cars and open to children’s play for four hours at a time. Just like Riverbend Park, the idea had to start small — temporary, built to address the needs of local residents, while planting the seed of more substantive change. The group eventually opened eight “playing lanes” throughout the city, created a replication manual for other neighborhoods, and generated data to advocate for more sustainable play space in the future.

In this way, a city might change its shape to adjust to its citizens’ changing needs. Multiple, imaginative uses of public space could be made from what’s already in front of us. In 2020, cities such as Philadelphia and Chicago also opened play streets for children in lieu of traditional indoor summer camps. But open streets for children could be more than just a stopgap amenity for pandemic emergencies.

A found park, a welcoming museum, streets that shift their shapes for children: These are designs built with time as the sculpting tool. Ordinary people like Isabella Halsted have been able to reshape time, and make our public spaces more truly public. What other worlds might be possible, inside or outside a pandemic? Who else might take up the cause of a small shift in the clock, a rescue of time outside the machine of efficiency?

Sara Hendren is an artist and design researcher, and a professor at Olin College of Engineering. She is the author of “What Can a Body Do? How We Meet the Built World.”

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