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Speaker 1: Welcome to brain Stuff production of I Heart Radio Pay

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Speaker 1: brain Stuff Lauren Boba blam here. If you've ever driven

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Speaker 1: west on Interstate A D through Nebraska, you've seen one

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Speaker 1: of the flattest and emptiest roads in America, and you

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Speaker 1: probably had some time to ponder life's most important questions.

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Speaker 1: For example, why is the highway called I A D anyway?

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Speaker 1: And why do different interstate names contain one or two

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Speaker 1: or three digits. Well, buckle up, because you're about to

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Speaker 1: learn about the codes behind the US interstate naming system.

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Speaker 1: But for starters, let's talk about how the interstate highway

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Speaker 1: system began. The formal name for these roadways is the

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Speaker 1: Dwight D. Eisenhower National System of Interstate and Defense Highways,

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Speaker 1: and the project was approved by Congress through the Federal

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Speaker 1: Aid Highway Act of ninety six that authorized the construction

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Speaker 1: of about forty one thousand miles or sixty six thousand

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Speaker 1: kilometers of highways stretching across the country from east to

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Speaker 1: west and north to south. One of the main purposes

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Speaker 1: of the interstate system was national defense. President Eisenhower had

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Speaker 1: served as the Supreme Commander of Allied Forces during World

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Speaker 1: War Two. In Europe and had witnessed the importance of

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Speaker 1: Germany's Autobahn network, which allowed for speedy transportation throughout the country.

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Speaker 1: Another slightly more ominous selling point the quick evacuation of

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Speaker 1: cities in the case of potential nuclear attacks. And of course,

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Speaker 1: the system was touted as a way for all Americans

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Speaker 1: to travel with fewer traffic jams and more efficient routes

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Speaker 1: with no at grade crossings, that is, intersections. The system

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Speaker 1: used overpasses and underpasses to allow for seamless, stop free,

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Speaker 1: high speed travel. There are now forty six thousand, eight

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Speaker 1: hundred and seventy six miles or seventy thousand, four hundred

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Speaker 1: and thirty nine kilometers of roadway within the interstate designation.

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Speaker 1: Construction began in nineteen fifty six in Missouri on what's

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Speaker 1: out named I seventy, but the system as a whole

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Speaker 1: wasn't completed until when crews finished a devilishly difficult stretch

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Speaker 1: in Glenwood Canyon, Colorado. There you'll find forty bridges and

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Speaker 1: viaducts on a single twelve mile or nineteen kilometer stretch.

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Speaker 1: The Interstate Highway System transformed American life. The cargo trucking

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Speaker 1: industry arose, gas stations and truck stops, blossomed, suburbs sprung

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Speaker 1: up around cities, and the concept of the road trip

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Speaker 1: entered the national lexicon. And as those road trippers zipped along,

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Speaker 1: some of them surely wondered why interstates have various numbering systems.

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Speaker 1: But why is one named I five while another is

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Speaker 1: I four eighty. Let's take a closer look at the

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Speaker 1: digits on those shield shaped white, red and blue signs.

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Speaker 1: The number of digits in the name tells you whether

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Speaker 1: an interstate connects more than one city, or if it

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Speaker 1: serves a single metropolitan area. Interstates with one or two

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Speaker 1: digits all interconnect several regions. Those with three digits, like

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Speaker 1: I to eighty five, on the other hand, are meant

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Speaker 1: to serve a single city and are called auxiliary interstate highways.

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Speaker 1: They connect to longer two digit highways. The last two

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Speaker 1: digits match the parent highway. For example, I four e

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Speaker 1: d in Omaha is a five mile stretch that connects

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Speaker 1: I e ight in Nebraska with I twenty nine in Iowa. Likewise,

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Speaker 1: the aforementioned I T eighty five circles Atlanta and connects

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Speaker 1: to I eight five going north and south. Continuing to

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Speaker 1: use that as an example, you can tell that I

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Speaker 1: A D five runs north to south because odd numbered

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Speaker 1: interstates move traffic north to south, while those with even

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Speaker 1: numbers stretch east to west. The numbering for east west

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Speaker 1: highways starts in the south and moves north, so I

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Speaker 1: ten anchors the bottom border Santa Monica, California, to Jacksonville, Florida,

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Speaker 1: and I ninety is near the country's northern border, a

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Speaker 1: Seattle to Boston. Meanwhile, for north to south running interstates,

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Speaker 1: numbering begins in the west, starting with I five parallel

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Speaker 1: to the west coast. The easternmost interstate is I N five,

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Speaker 1: running on the east coast from Maine to Miami. There

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Speaker 1: are some rare exceptions to this pattern in cases where

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Speaker 1: stretches of road were added after the first framework was

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Speaker 1: already in place. For example, I N nine didn't receive

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Speaker 1: its interstate designation until and so it lies to the

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Speaker 1: west of There are only two places across the country

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Speaker 1: where interstates split as they moved through major cities, both

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Speaker 1: on I thirty five, one around the Minneapolis St. Paul

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Speaker 1: metro area and the other to go through Dallas and

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Speaker 1: Fort Worth. Meanwhile, the first digit of a three digit

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Speaker 1: interstate tips you off to its purpose. Connectors or spurs

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Speaker 1: that only intersect one time mostly receive odd numbered first digits.

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Speaker 1: Even numbered first digits, how ever, tend to be bypasses

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Speaker 1: and loops that intersect with their parent interstate in two locations.

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Speaker 1: The names of major interstates are never repeated. They're always unique. However,

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Speaker 1: some lesser stretches do use the same two digit numbers.

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Speaker 1: For example, both New York and North Carolina have an

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Speaker 1: I eighty seven. There are also I seventy six is

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Speaker 1: in both Colorado and Pennsylvania. Three digit interstates, however, can

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Speaker 1: be used as often as necessary throughout the country, although

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Speaker 1: they can't be repeated in a single state. But this

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Speaker 1: numerical interstate system can get even messier. For instance, in

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Speaker 1: San Francisco, there's I to thirty eight, even though there's

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Speaker 1: no I thirty eight for it to connect to. Instead,

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Speaker 1: it's an artery between I e eighty and I five eight.

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Speaker 1: But because California already had so many roads, the more

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Speaker 1: appropriate digits were already in use with other roadways, and

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Speaker 1: there are other exceptions to Alaska, y E, and Puerto

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Speaker 1: Rico all have interstates Even though these roads don't connect

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Speaker 1: to other states, they have special lettered designations. Alaska has

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Speaker 1: A one through A four Hawaii and H one through

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Speaker 1: H three in Puerto Rico PR one and PR two,

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Speaker 1: and state highway naming convention differs a bit from the interstates.

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Speaker 1: These roadways, which are denoted by black and white signs

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Speaker 1: with badge symbols, use the same system of odd numbers

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Speaker 1: for north south routes and even numbers for east west routes. However,

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Speaker 1: the number system is flip flopped. The numbers on east

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Speaker 1: west roads gets smaller as you go from south to north,

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Speaker 1: and the numbers on north south highways increase as you

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Speaker 1: go from east to west across the state. Meanwhile, I

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Speaker 1: ninety is the longest U S inter state, stretching all

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Speaker 1: the way from Boston to Seattle and covering nearly three thousand,

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Speaker 1: one hundred miles or five thousand kilometers, traverses thirteen states,

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Speaker 1: and I, which connects Miami to Maine, cuts through the

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Speaker 1: most states of all the Inner States fifteen, and it

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Speaker 1: also goes through Washington, d C. Today's episode was written

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Speaker 1: by Natan Chandler and produced by Tyler clang Or. More

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Speaker 1: on this and lots of other numerous topics. Visit how

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Speaker 1: stuff works dot com. Brain Stuff is production of iHeart

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