Cities in the United States are known for the rigid gridiron pattern, you can see this in cities like New York, Chicago and San Francisco. It was the way city streets were planned for over a century, but that changed in the 1930s and 1940s as new development came with a new street pattern, loops and cul-de-sacs.
New neighborhoods are barely connected to one another, this street pattern became one of the defining characteristics of urban sprawl. Why did we change how we designed our street networks?
Ever since the land ordinance of 1785, the united states embraced the grid. The law divided much of the United States into square mile grid cells and later Acts extended the grid all the way to the Pacific. The cities followed suit, either using those national grids as a starting point, or designing their own grid, often matching the local topographic and geographic features.
Grids made it easy to subdivide and sell land perfect for a rapidly expanding country. If grids were so great, why did we switch to the disconnected networks? We didn’t switch all at once, there was a brief transition period from about 1900 to 1930, those dates correspond to the growth and development of the automobile as well as when the streetcars were most popular.
Streetcar suburbs were typically laid out in the same grid pattern that made land speculation so easy. It also made it easy for people to walk to nearby streetcar stops, but as cars became more popular real estate developers could design neighborhoods often referred to as subdivisions that didn’t need to be near streetcar stops. These new subdivisions could also be smaller, as they didn’t have to pay for the cost of a streetcar line. What you got were smaller more irregular subdivisions in odd places.
The roads and these subdivisions would often not connect to each other and the road networks were often not as well thought out. Cities at the time didn’t have any way of forcing developers to design better street systems or cooperate with each other. The federal government eventually drafted a standard city planning Enabling Act in 1928 that states adopted. These rules allowed cities to adopt citywide street plans and regulate the design of subdivisions.
So that tells us why we moved away from the grid, but it doesn’t tell us how we got to the loops and the cul-de-sacs of today. Subdivision regulations found in cities don’t explicitly say that new residential areas have to have loops and cul-de-sacs. So what happened next, the Great Depression happened, suddenly you had a lot of people who needed affordable housing and a shaky banking system that was often unwilling or unable to make loans to home buyers and housing developers. This is where the federal government stepped in and created the Federal Housing Administration.
The FHA would underwrite the loans of new housing developments making the investment less of a risk to bankers, but they would only underwrite sound investments and they considered the design of the subdivision when making that determination.
This put the FHA in a position of significant power over suburban residential design. Developers didn’t put up a fight and went along with the FHA subdivision design recommendations. So what did they recommend? The hot new planning trend at the time was called the neighborhood unit. The basic features of the neighborhood unit are a size that matches the attendance boundary for an elementary school located at the center of the neighborhood, busy streets at the edges with no through traffic.
In smaller neighborhoods, streets shops located on the edges along busy streets with libraries and parks in the interior. No gridiron, but instead, streets designed to connect to places where people wanted to go, you can sort of see how the neighborhood unit gets us closer to suburban sprawl street patterns. Imagine strip malls along those suburban arterial streets.
Real estate developers design their subdivisions according to neighborhood unit principles to get the funding they needed for their housing. The result was a lot of disconnected networks that didn’t connect the way they used to with the grids, but this doesn’t explain cul-de-sacs. Where did they come from? They first made an appearance in the garden cities era from about 1900 to 1935. They were designed as a refuge from streets that were increasingly full of loud fast moving cars.
Street patterns with a lot of cul-de-sacs use less asphalt and concrete which save developers money and because they only handle local traffic, cul-de-sacs could be narrower, another win for developers. Despite the benefits of cul-de-sacs, it took a while for them to catch on. They weren’t even prominently used in example neighborhood unit communities. Their popularity comes from a pretty mundane source engineering design standards.
Transportation engineering emerged as a separate field from civil engineering in the 1920s, and in 1931 thirty engineers got together to form the Institute of Transportation Engineers. This organization is notable for publishing design standards for the road building industry. They became the design manuals engineers grabbed when they laid out subdivisions.
ITE in its 1965 publication recommended practice for subdivision streets, recommended that subdivisions should discourage through traffic, four-way intersections should be avoided in favor of key intersections. Curvilinear patterns loops and cul-de-sac should be used to encourage slow-moving traffic. T-intersections were encouraged because of an engineering study that compared crash rates between gridded neighborhoods and FHA’s unit neighborhoods. The study found that there were almost eight times the crashes in gritted networks. They also found that T-intersections had no crashes at all. They concluded that for safety’s sake neighborhoods should be full of cul-de-sacs, T-intersections and convoluted street patterns.
Subsequent updates through 1990 did little to change these recommendations. The period between the first publication in 1965 and 1990 saw a huge residential building boom in the United States and engineers at the time used those ITE standards.
So that’s how we got from the gridded streets of the 19th century to the disconnected mess of today. This is primarily a result of the institutionalization of street design standards, first by the federal government and by industry organizations. Once something becomes standard practice, it’s really hard to change.
You may have noticed that this article mentions disconnected street patterns in somewhat negative tone, and that’s because building streets like this makes it really hard to use any kind of transportation option besides a car. Circuitous streets make walking and biking trips longer which can discourage people from doing so.
Thankfully, cities have begun to rethink their subdivision street design standards and we’re seeing networks with more connections for pedestrians and cyclists. The next phase of residential street design could be some sort of hybrid or cul-de-sac still exist because people love to live on them. But there are paths for other modes, some places already have these path systems and it’s something we could see more of in the future.