This piece is part of the Sidewalk Talk series “15 Innovations That Shaped the City.”
Square-block street grids are a fixture of modern urban life—as unremarkable as the clouds in the sky—and they’re rooted in far more planning than most people ever notice. From street width to block lengths, grid choices deeply affect the look and feel of our neighborhoods, and how we navigate them. They also determine how well a city can adapt to the times: once built, a street grid must support changes in transportation systems, building patterns, and infrastructure, while never losing its basic shape. Far from a static, boring layout choice, the grid is increasingly becoming a dynamic platform for cities—a process that will only accelerate as new tools come into use.
Grid-patterned streets appeared in some of the earliest cities on record. Excavations in the Indus Valley of modern-day Pakistan and northern India have found gridded streets dating back some 5,000 years. The Arthashastra—a Sanskrit text dating back 3,000 years—required cities to be divided by three north-south and three east-west streets to create consistency in living arrangements.
Other grid patterns appeared in cities of Babylon, China, Egypt, and the Mesoamerican cultures of Mexico. Structure and predictability was the primary theme. Romans, for instance, used grids in their military camps, called castra, to ensure that soldiers were able to find their place and efficiently continue daily routines even in a new location.
But while some historical cities were planned on grids, many others were not. A majority of cities in both Europe and Asia developed organically, with local property owners arranging streets and sidewalks, and most retain their shape today. Other geometric plans were also used for either aesthetic or defensive reasons, such as the quadrant system of Washington, D.C., which features radial major avenues embedded into a grid.
The grid concept was adopted at a rapid rate during the growth of the American colonies, beginning with Philadelphia. Founder William Penn, a fervent Quaker, used the even spacing of the grid to enact his principles of equality and community, including four public squares that are still landmarks of the city today.
Besides creating evenly sized lots, grids also led to more predictability for buyers and builders, a trait that endeared them to city planners. In 1811, New York City leaders approved a plan for a strict grid pattern on the upper part of Manhattan after some 200 years of organic street development in the lower part of the island. The conversion showed that grids aren’t as easy to implement as they look: surveyor John Randel spent a decade creating a detailed map, traversing the island on foot, and dealing with irate homeowners in the grid’s planned path, according to the journalist Marguerite Holloway, who chronicled Randel’s effort in The Measure of Manhattan.
“The simple gridiron pattern of straight streets and rectangular blocks established itself as the primary basis for American city form,” wrote urban historian Edward Spann.
Rural areas also got the grid treatment, particularly in the rapidly expanding West, which followed new railways. Much like city officials, railroad owners saw that grids could make development faster and more predictable, allowing them to place new towns every 20 miles along along thousands of miles of rail. “They’d come to the town and lay out their template around the station,” says Norman Garrick, an associate professor of civil engineering at the University of Connecticut.
The main benefit of an urban street grid is its power of standardization and simplification. Travelers can get around without studying the system; indeed, today, 61 percent of U.S. cities use downtown street numbering systems modeled on the grids of Philadelphia and New York. Buyers can purchase lots—sometimes sight unseen—knowing exactly what they’ll get. Infrastructure engineers need only to plan for straight and 90-degree pipes, making repairs easier and more predictable. Transportation agencies can provide new services along established corridors.
Grids also create the conditions for vertical development and urban density. In the case of New York, the 1811 grid transformed 11,000 acres of unorganized land into 2,000 neatly defined blocks and hundreds of miles of street frontage, according to Spann. Developers welcomed the orderly property lines, easier land sales, and access to buildings; retailers welcomed the short (200-foot), walkable block lengths. “The public plan thus provided a stable, assured basis for private planning,” writes Spann.
Other street patterns have ruled specific periods of urban development. In the 1950s, many cities built freeways over their grids and designed suburbs centered around inaccessible cul-de-sacs—deviations that, in retrospect, have highlighted the grid’s benefits. In cities dominated by hub-and-spoke freeways and suburbs, fewer people walk or bike, transit systems lose their utility, and traffic jams become a fixture of city life. Today, many cities are considering tearing down urban freeways and reintegrating the streets back into the surface grid.
Planners are getting better at making changes within a city’s existing grid structure. They now rely heavily on modeling software, which uses reams of data—on expected home and workplace locations, public transit, traffic, and so on—to generate analyses based on preferred criteria, such as communities that encourage walking. As that data improves, through real-time collection and machine-learning, it becomes possible for planners to learn what’s working and what isn’t on an accelerated timeline.
The emergence of self-driving vehicles also enables cities to reimagine their street grids, since they require dramatically less street space devoted to parking and don’t rely on intuitive navigation. Planners may be able to reclassify streets based on traffic flows, with high-speed vehicle traffic forced to the perimeter and interior streets reoriented around bikes, pedestrians, and place-based activities. They can reclaim curb space can be reclaimed for other uses. They might even spread development more evenly across a neighborhood, rather than adhering strictly to transit hubs.
The grid may look simple to an undiscerning eye, but these age-old physical platforms create the conditions for our cities to evolve in the digital age.