How do we define Tri-Interstate Cities? 3 different 'parent'/2di interstates?
So we currently have:
San Diego (5, 8, 15), Denver (25, 70, 76), San Antonio (10, 35, 37), Fort Worth (20, 30, 35W), Dallas (a 'quad': 20, 30, 35E, 45), Houston (10, 45, 69), Oklahoma City (35, 40, 44), Kansas City (29, 35, 70), Maidison (39, 90, 94), Quad Cities (74, 80, 88), Chicago (a 'quint': 55, 57, 88, 90, 94), Bloomington (39, 55, 74), St Louis (quad: 44, 55, 64, 70), Champaign (57, 72, 74), Memphis (quad: 22, 40, 55, 69), Slidell (10, 12, 59), Birmingham (quad: 20, 22, 59, 65), Atlanta (20, 75, 85), Chattanooga (24, 59, 75), Nashville (24, 40, 65), Louisville (64, 65, 71), Cincinnatti (71, 74, 75), Indianapolis (quad:65, 69, 70, 74), Gary (quad:65, 80, 90, 95), Detroit (75, 94, 96), Toledo (75, 80, 90), Cleveland (quad: 71, 77, 480, 90), Charlestown (64, 77, 79), Bedford (70, 76, 99), Harrisburg (76, 81, 83), Baltimore (quad:70, 83, 95, 97), DC (66, 270, 95), Columbia (20, 26, 77), Greensville (40, 73, 85), Scranton (quad:476, 380, 81, 84), Binghampton (81, 86, 88), Newark (78, 280, 95), New York (quad:78, 80, 87, 95), Boston (90, 93, 95)
Future ones would include Casa Grande (8, 10, 11), Texarkana (30, 49, x69), Shreveport (20, 49, 69), Meridian (20, 59, 85) and Milwaukee (43, US41, 94).