A divided highway consisting of 4 lanes or more. What sets an Interstate apart from a 4-lane US Highway is the fact that the only way to get onto or off an Interstate is by way of an entrance or exit ramp, respectively. Construction of the first Interstate began in 1956 in St. Louis, Missouri.

The interstate highway system connects most of the major cities in the US with a single network of roads.

The numbers of United States interstate highways are laid out roughly in a grid.

Among one and two-digit numbers:

  • Even numbers are assigned to highways that run roughly east-west
  • Odd numbers are assigned to highways that run roughly north-south.
  • Numbers that end in 0 or 5 are intended to be the major interstates that reach a large part of the way across the country.
  • The numbers of east-west highways are smallest in the south, and roughly increase as you move north.
  • The numbers of north-south highways are smallest in the west, and roughly increase as you move east.
As a result, I-10 is the southernmost major interstate highway, stretching from southern California to Florida. I-90 goes from near Seattle, Washington to Boston, Massachusetts, after making a bit of a detour around the Great Lakes. I-5 and I-95 run along the west and east coasts, respectively, connecting the ends of interstates 10 and 90, though 95 continues on up into Maine.

Three digit interstate highway numbers are assigned to local roads which connect a city to the interstate highway system. These fall into two categories:

  • Loop roads circle around a city or metropolitan area, or connect one main interstate highway with another, and have numbers beginning with an even digit.
  • Spur roads, which branch off the main interstate and head into nearby cities, and have numbers beginning with odd digits.
The last two digits in the numbers of both of these types of highways are taken from the number of the associated main interstate highway. For instance, I-410 is a loop around the central part of San Antonio, Texas, meeting I-10 on both sides. I-535 is a spur which leaves I-35 at Duluth, Minnesota and goes to Superior, Wisconsin.

Also note that these three-digit interstate numbers are not unique; since their nature as local roads restricts them to one or two states, the numbers are often reused in other states. There are seven separate I-295s running through a total of 9 states.

There are exceptions to every rule, due in part of the fact that roads have to be built to accommodate both natural and human geography.

  • I-69 is the planned NAFTA super-highway to run from Mexico to Canada; it does not end in a 5 because:
    • All the x5 numbers are already used.
    • The road is an extension of the existing interstate 69, which is currently a relatively short interstate.
    • At the south end, in Texas, it also deviates significantly from the usual pattern of numbering; the north-south interstates in Texas typically have numbers in the 30s and 40s. At the north end the numbering looks sensible.
  • Many of the Loop/Spur distinctions are blurred or just plain wrong.
  • A more extreme rule violation is I-238 in California.


fast fiction

"...and the I stands for INTERSTATE, anybody remember that..." The voice faded in from the night and dopplered out back again, underscored with a snarling moan that was unfamiliar. They gathered to listen, drawn from the lawns and televisions, moving slowly up from armchairs and webcliners, away from the screens. A couple of them stopped JoniDeere(tm)'s and stepped off the silently cheery electrimowers, moving with the crowd as it swayed slightly towards the almost-forgotten chainlink fences down the street where the overpass was. The roar was almost gone, with only the anemic sound of MetroCopper(tm) SirenAlarms wavering by in what must have been pursuit, the eager humming of mini-donuts on crazed concrete thrashed by dozens of rare earth cells rising. A swarm of bees blindly staggering after the interloper who'd fucked their queen and flown on, laughing, dragging her pheromones in a trail of fury-inducing mania. When nothing more happened, and the noises faded, they returned to their homes and weblinks and evening dinoblogs and dinners.

Of course, it returned the next night.

This time, the MewsNews had it first, warning of dangerous transport terrorists, telling all good cits to stay off the Road. A few had figured it out, though, and this time, there were several standing at the chain link, fingers locked through the rusting barrier, when the enigma came. Rising in the distance, a sound that not many knew and all wondered at, overlaid with the warbling fed-back tones of anger and fury:

"WATCH LISTS! What the fuck...you SHEEP! Any of you ever left the fucking town? ANY? Any of you been on the fucking road? Call yourselves AMERICANS, they kick you off the AIRPLANES, then they kick you off the TRAINS, they kick you off the BUSES, they tell you to stay in your fucking SUBURBS, tell you it's SAFER, LOOK AT YOU, just LOOK AT YOURSELVES..."

...and it was gone again, few futile struggling minions in electric pursuit.

The third time, the last time, the entire block was there, their hands pressed to the fences and their Footballoculars(tm) ready, with SnapCams poised and coolers near their chairs. A few MetroCoppers had their Cushmans set up to block the Road, this night; SirenLarms off, they waited in eager glee while several of their colleagues tried vainly to convince the watching throngs to return to their living rooms and leave the browned-out scrub from the overpass of the Great 405.

The voice wavered into existence again, from off in the heat-hazed gullies of thermocrete and jersey barriers: "...1920s told us all, motherfuckers, told us what it was about, Henry motherfucking Ford and the fucking saints, Saint Packard and Saint Shelby, Archbishop Petty and Rabbi Brabham, boys, where've you fucking been? Where've you gone, and where'd we let you go? It's a precious resource, they say, national fucking crime to not turn it in for scientific research - well fuck that, it's a crime they're not researching how to make more, boys, because there's only one fucking thing it's good for-"

A squawk as the black fugitive shot over the hill to see the MetroCopper carts blocking the Road, but it didn't slow at all, merely upped its snarling shout. The crowd gasped, but before anything could happen before them, there was an explosion of noise-

They turned as one-

A garage door breaking into flinders, a Lawn shredding itself into the sky-

Another shape-

With a screeching bang, the chainlink slammed down. The silver and red demon bowled over the two MetroCarts blocking the two clear lanes of Road, just tore through them from the back side, bowled them over, before sliding to a stop. The oncoming shape spun halfway, screamed at the heavens and stopped as well, door to door, treating the onlookers to the long-forgotten smell of melted rubber. There was a moment of burbling engine noise, then-

"All fucking right."

One after the other, the two free cars shot through the barrier and vanished into the Interstate, leaving behind nothing but long strips of rubber and the wailing outrage of a gasoline dream.

In"ter*state` (?), a.

Pertaining to the mutual relations of States; existing between, or including, different States; as, interstate commerce.


<-- interstate commerce n. commerce that involves transportation of articles of commerce across state lines [U.S.]. interstate commerce commission. The governmental commision charged with making and enforcing regulations concerning interstate commerce. -->


© Webster 1913.

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