In America, we have a compulsion to rank things. Top ten lists, March Madness, salary surveys, and all sorts of other competitions and studies help us determine who's number one and who are the losers.
Even highways are not immune to this: but the number of variables involved in comparing highways can lead to intractable disagreements unless you limit the discussion to such easily measured values as number of lanes or miles. Something as vaporous as "most prominent" or "most important" highway can't be determined to everyone's satisfaction.
In 2001, I developed a Perl script that assigns numerical values to various attributes of each 2-digit interstate highway. The end result: a ranking in decreasing order of prominence. The most important highway turns out to be Interstate 95 ("so easy to use, no wonder it's number 1!"). The beauty of this approach is that numbers don't lie and the results are undisputable.
Too bad the study is flawed; I'm demanding that you accept my assumptions (see below) as golden: having attribute X is worth Y points, and so on. This rhetorical tactic is not all that uncommon in any sort of debate. However, you can download the script, adjust the parameters as you see fit, and generate new results. The script first prints out the parameters, then lists how each interstate fared.
In January 2018, David Raucci contributed a Python port of the Perl script, including a few data corrections and information for several new interstates (14, 22, 41 and more).
Here are the results from the Python script. I-95 is the most important interstate, while North Carolina's I-87 is the one least likely to be missed. Flame on!
Kurumi's Interstate Ranker (2018 results) Scoring: Each mile in length: 1 Each state occupied: 200 Each international border touched: 100 Each major 2di generated: 200 Each minor 2di generated: 100 Each major 2di intersected: 100 Each minor 2di intersected: 50 Each 3di it's a parent of: 150 Each 1M pop in metro areas served: 100 I-95: 16376 I-80: 14300 I-90: 12070 I-10: 11360 I-75: 8536 I-70: 8364 I-5: 7181 I-94: 6935 I-35: 6869 I-40: 6705 I-20: 5689 I-15: 5634 I-55: 5314 I-65: 5237 I-69: 4905 I-85: 4469 I-64: 4254 I-81: 3905 I-78: 3544 I-77: 3360 I-87n: 3333 I-76e: 3234 I-29: 2751 I-25: 2513 I-74w: 2464 I-71: 2445 I-57: 2436 I-30: 2367 I-45: 2335 I-44: 2283 I-84w: 2220 I-59: 2195 I-91: 2090 I-41: 1876 I-24: 1866 I-93: 1840 I-26: 1806 I-96: 1742 I-84e: 1732 I-79: 1693 I-49: 1588 I-88w: 1391 I-8: 1348 I-39: 1206 I-83: 1135 I-22: 1113 I-66: 1076 I-76w: 1037 I-4: 1032 I-17: 946 I-89: 941 I-72: 879 I-82: 844 I-86e: 834 I-74e: 822 I-43: 792 I-37: 743 I-16: 717 I-99: 699 I-73: 632 I-68: 613 I-19: 564 I-12: 536 I-88e: 518 I-2: 447 I-27: 424 I-97: 418 I-86w: 413 I-14: 326 I-87s: 310