List of Interstate Highways
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Primary interstates are the major interstate highways of the United States and are assigned a one or two-digit route number. Even route numbers are assigned to east/west routes, with the lower numbered routes being further south (I-10) and higher numbered routes in the north (I-90). Similarly, odd route numbers are assigned to north/south routes, with the lower numbered routes being further west (I-5) and the higher numbered routes being further east (I-95).
Three-digit interstates are spur or loop interstates that usually service large cities and suburbs. The last two digits of a three-digit interstate are always the number of the parent route, the primary interstate where it originated. If the first digit is odd, the interstate is typically a spur route while if the first digit is even, the interstate is typically a loop route. Three-digit interstates are covered in their parent route's article, and those that have their own articles are linked below. (In the table below, interstates designated with an asterisk are "secret" interstates -- that is, they are not signposted as interstates.)
- Notable exceptions to these numbering standards are Interstate 238 in California and Interstate 99 in Pennsylvania.
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Primary Interstates
Hawaiian Interstates
The interstate highways in Hawaii are signed with the standard Interstate shield, with the letter "H-" prefixed before the number. They are fully controlled-access routes built to the same standards as the mainland Interstate routes.
- Associated route: I-H-201
- Missing image
InterstateH2.png
Interstate H-2 
Interstate H-3
Alaskan and Puerto Rican Interstates
The Federal Highway Administration (http://www.fhwa.dot.gov/) funds four routes in Alaska and three routes in Puerto Rico under the same program as the rest of the Interstate Highway system. However, these routes are not required to meet the same standards as the mainland routes:
- "Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway." [1] (http://www.fhwa.dot.gov/reports/routefinder/index.htm)
Alaska's "Interstates" are unsigned, though they all have state highway numbers (which don't match the Interstate numbers).[2] (http://www.alaskaroads.com/Interstate-ends.htm)
Like Alaska, Puerto Rico signs its "Interstates" as territorial routes, and the numbers do not match their official Interstate designations. However, many of the territory's routes are freeway-standard toll roads.[3] (http://www.hawaiihighways.com/Puerto-Rico-page2.html)
| Template:Ed divPrimary Interstate Highways | Missing image Interstate_blank.png Interstate Highway marker | ||||||
| 4 | 5 | 8 | 10 | 12 | 15 | 16 | 17 |
| 19 | 20 | 22 | 24 | 25 | 26 | 27 | 29 |
| 30 | 35 | 37 | 39 | 40 | 43 | 44 | 45 |
| 49 | 55 | 57 | 59 | 64 | 65 | 66 | 68 |
| 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 (W) |
| 76 (E) | 77 | 78 | 79 | 80 | 81 | 82 | 83 |
| 84 (W) | 84 (E) | 85 | 86 (W) | 86 (E) | 87 | 88 (W) | 88 (E) |
| 89 | 90 | 91 | 93 | 94 | 95 | 96 | 97 |
| 99 | 238 | H-1 | H-2 | H-3 | |||
| Unsigned Interstate Highways | |||||||
| A-1 | A-2 | A-3 | A-4 | PRI-1 | PRI-2 | PRI-3 | |
| Lists Two-digit Interstates - Three-digit Interstates Gaps in Interstates - Intrastate Interstates Interstate standards - Proposed Interstates | |||||||
External links
- Alaska Roads - Interstate ends photos (http://www.alaskaroads.com/Interstate-ends.htm)
- Puerto Rico road photos (http://www.hawaiihighways.com/Puerto-Rico-page2.html)
- The Dwight D. Eisenhower National System of Interstate and Defense Highways Route Log and Finder List (http://www.fhwa.dot.gov/reports/routefinder/index.htm)
- 3-digit Interstate Highways (http://www.kurumi.com/roads/3di/index.html)