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Cities in the United States are known
for their 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 barely connected to one another either.
This street pattern became one
of the defining characteristics of urban sprawl.
Why did we change how we designed our street networks?
(bicycle cell chiming)
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.
Cities followed suit.
Either using those national grids as a starting point
or designing their own grid,
often match a local topographic and geographic features.
Grids made it easy to subdivide and sell land,
perfect for a rapidly expanding country.
I have a whole video on this topic
of grids, if you want to go check it out.
If grids were so great,
why do we switch to the disconnected networks we build now?
Well, for one thing, 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 street cars 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 street car line.
What you got were smaller, more irregular
subdivisions in odd places.
The roads in 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 state's adopted.
These rules allowed cities to
adopt citywide street plants
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.
Most subdivision regulations founded
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.
Here's a sample neighborhood.
The basic features of the neighborhood unit are
a size that matches the attended boundary
for an elementary school
located at the center of the neighborhood,
busy streets at the edges with no through traffic,
and smaller neighborhood streets.
Shops located on the edges along busy streets
with libraries and parks on the interior,
no grid iron 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 designed 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?
Cul-de-sacs 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 used less asphalt
and concrete, which saved developers money.
And because they only handled local traffic
cul-de-sacs could be narrower,
another win for developers.
Despite the benefits of cul-de-sacs
and their use in some influential Garden City projects,
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, 30 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.
The 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 T intersections.
Curvilinear patterns, loops, and cul-de-sacs should be
used to encourage slow-moving traffic.
T intersections were encouraged because
of an engineering study that compared crash rates
between grided neighborhoods
and FHA neighborhood unit neighborhoods.
The study found that there were almost eight
times the crashes in grided 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 grided 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,
then by industry organizations.
Once something becomes standard practice,
it's really hard to change.
Now, you may have noticed in this video I talk
about these disconnected street patterns
with somewhat of a negative tone,
and that's because building streets like this
makes it really hard to
to use any kind of transportation option besides a car.
Circuitous streets make walking and biking trips longer
which can discourage people from doing that at all.
Grids are far more flexible.
You can turn grids into cul-de-sacs,
but it's a lot harder to take
down houses to turn cul-de-sacs into grids.
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 where cul-de-sacs still exists
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.
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