If you ’ve ever push back west on Interstate 80 through Nebraska , you ’ve seen one of the flattest and emptiestroadsin America … and you probably had some metre to mull over life ’s most crucial questions . For example , why is the highway called " I-80 , " anyway ? And why do some interstate names have one , two or three digits ?
clasp up , you ’re about to find out the hush-hush code behind the U.S. interstate naming system .
But for starters , allow ’s find out how the Interstate Highway System start . The formal name for these roadways is TheDwight D. Eisenhower National System of Interstateand Defense Highways , and the project was okay by Congress through the Federal Aid Highway Act of 1956 . It empty the construction of about 41,000 mile ( 65,983 kilometers ) of highways , debase across the country from east to west and due north to Confederate States of America .
One of the chief purposes of the interstate organisation was internal defense . President Eisenhower had serve as the Supreme Commander of Allied Forces during World War II in Europe , andhe’d witness the grandness of Germany ’s Autobahn web , which allowed for speedy DoT throughout the state .
Another , more ominous selling power point ? The quick evacuation of cities thatsuffered potential atomic attacks .
And of line , the scheme was touted as a way for all Americans to journey with few traffic crush and more efficient routes . With no at - grade intersection ( that is , intersections ) , the system of rules used overpasses and underpasses to allow for unseamed , break off - free , in high spirits - speed locomotion . There are now 46,876 international nautical mile ( 75,439 kilometers ) of roadway with the interstate denomination .
Construction start in 1956 in Missourion what ’s now named I-70 , but the system as a whole was n’t completeduntil 1992 , when crowd finish a fiendishly difficult stretch in Glenwood Canyon , Colorado , where you ’ll retrieve 40 bridges and viaduct on a single 12 - mile ( 19 - kilometre ) stretch .
The Interstate Highway System transformed American spirit . The load trucking industry arose , gas stations and hand truck stops blossomed , suburbs bound up around metropolis , and the concept of the " route slip " entered the national lexicon .
And as those road trippers zipped along , some of them sure wondered why interstates have various enumeration scheme . Why is one named I-5 while another is I-480 ? permit ’s take a close look at the digits on those red , bloodless , and downcast cuticle - shaped sign .
Those Highway Numbers Aren’t Random
Thenumber of digits in the nametells you whether an interstate link more than one city , or if it serves a unmarried metropolitan area . Interstates with one or two digits ( e.g. , I-95 ) interconnect several regions . Those with three digits ( e.g. , I-285 ) , on the other paw , are imply to serve a individual city and are call auxiliary interstate main road . They join to longer two - digit highways . The last two finger match the parent highway – for example , I-480 in Omaha is a 5 - air mile reaching that connects I-80 in Nebraska with I-29 in Iowa . Likewise , I-285 circle Atlanta and unite to I-85 , going north and south .
Even - number interstates stretch out east - west , while those with leftover numbers move dealings magnetic north - south . Numbering for east - west main road start in the southward and move north , so I-10 ground the bottom border ( Santa Monica , California , to Jacksonville , Florida ) , and I-90 is near the country ’s northerly molding ( Seattle to Boston ) .
For north - due south interstates , numbering begins in the Dame Rebecca West , starting with I-5 , parallel to the West Coast . The eastmost interstate is I-95 , running on the East Coast , from Houlton , Maine , to Miami .
There are some rare exceptions to this radiation diagram , in cases where stretches of route were added after the first framework was already in place . For example , I-99 did n’t receive its interstate appellation until 1998 , and it lies west of I-95 in easterly Pennsylvania .
Just two interstates splitas they move through major urban center . One is I-35E and I-35W in Minneapolis - St. Paul metro area ; the other is I-35E and I-35W , which move through Dallas and Fort Worth , respectively .
The first finger of a three - finger’s breadth interstate tips you off to its role . Connectors or spurs that only intersect one time mostly receive odd - numbered first digits . Even - numbered first digits , however , incline to be bypasses and loop that intersect with their parent interstate in two location .
The name of major interstates are never repeated ; they are always unique . However , some lesser stretches apply the same two - digit numbers . For representative , both New York and North Carolina have an I-87 . There are also I-76s in both Colorado and Pennsylvania .
Three - digit interstates , however , can be used as often as necessary throughout the country , but they ca n’t be repeated within a single state .
The Numerical Interstate System Can Get Messy
For instance , in San Francisco there ’s I-238 , even though there ’s no I-38 for it to unite to – instead , it ’s an arteria between I-880 and I-580 . But because California already had so many route , the appropriate digits were already in use with other roadways .
There are other exceptions , too . Alaska , Hawaii and Puerto Rico all have interstate highway , even though these roads do n’t link to other United States Department of State . They have particular lettered designations : Alaska has A1 through A4,Hawaii has an H1 through H3and Puerto Rico has aPR1 and PR2 .
State highwaynaming conventiondiffers a bit from the interstates . These roadways , which are denoted by bleak - and - white signs with badge symbol , practice the same organisation of odd numbers for north - Confederate States routes , and even numbers for eastward - west routes . However , the number system is flip - flop . The numbers on east - west roads get bombastic as you go from Second Earl of Guilford to Confederacy , and the numbers on north - south highways increase as you go from east to Cicily Isabel Fairfield across the state .
