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      Mechanix Illustrated - April 1977 - bottom half of pg 21

Interstate Numbers Game

    Play the numbers game offered by the neighborhood bookie and you'll
probably lose.  Play our numbers and you can win every time.  We call our
deal the Interstate Highway System Numbers Game.

    Knowing Interstate numbers can save you feul and get you there
faster--and safer too.  The 55-mph speed limit could give motorists
fabntastic feul thrift.  Execpt, of course, almost nobody observes it.  
MI has calculated the average Interstate speed at arround 62 mph.  Even
so, this figure is more economical than the stop-and-go of the minor
highways and streets.  The safty factor is quite clear: The accidental
death rate on the Interstates is 44percent lower than the overall average.

    To make the best use of the Interstate Highway System, you should
understand the basis of the numbering system.

    Main Interstate routes are numbered with one or two digits, with the
lowest number in the West and South. Odd-numbered routes running
south-north; evens, west-east.

    For eample, I-5 is the western-most, main north-south Interstate route
in the continental U.S., traversing California, Oregon, and Washington.  
On the other side of the continent, I-95 from Maine to Florida is the
eastern-most route and has the highest number.

    Crosscountry (east-west) routes start with I-10 in the South and
continue to I-90 in the North.

    In a few cases an Interstate route sprits into parallel or diverging
branches.  I-35 in Texas is a good example, dividing into two main
highways, with I-35E in Dalas and I-35W in Ft. Worth.  Later, the routes
join again as I-35.

    Partial or full circumferential or belt roads that connect with main
Interstates at the edge of a metropolitan area have threee digits, using
the main number with an even prefix.  For example, the Capitol Beltway,
circling Washington, D.C., and connecting with main north-south route
I-95, is I-495.  Atlanta's I-285 is another example.

    Supplementary radial or spur highways leaving a main Interstate and
deadending in an urban area also have a three-digit number, using the same
number as the main road with an odd prefix.  Thus, I-195 leaves I-95 in
Providence, R.I., and ends in New Bedford, Mass.  Likewise I-180 to
Peoria.

    You see, this numbers game is easy as 1-2-3.  Seatbelts, all!  *