How freeways are numbered:
- Routes with odd numbers run north-south.
- Routes with even numbers run east-west.
- For north-south routes, the lowest numbers are in the west.
- For east-west routes, the lowest numbers are in the south.
So, I-5 runs north-south along the west coast, while I-10 runs east-west in the south.
The major transcontinental routes are:
| East-west Transcontinental Routes | |||
| Interstate # | From | To | Distance |
| I-10 | Los Angeles, CA | Jacksonville, FL | 2,459.96 mi (3,959 km) |
| I-80 | San Francisco, CA | Teaneck, NJ | 2,906.77 mi (4,678 km) |
| I-90 | Seattle, WA | Boston, MA | 3,085.27 mi (4,965 km) |
| North-south Transcontinental Routes | |||
| Interstate # | From | To | Distance |
| I-5 | San Diego, CA | Blaine, WA | 1,382.04 mi (2,224 km) |
| I-15 | San Diego, CA | Sweetgrass, MT | 1,436.89 mi (2,312 km) |
| I-35 | Laredo, TX | Duluth, MN | 1,831.43 mi (2,947 km) |
| I-55 | New Orleans, LA | Chicago, IL | 943.69 mi (1519 km) |
| I-65 | Mobile, AL | Gary, IN | 888.08 mi (1,429 km) |
| I-75 | Miami, FL | Sault Ste Marie, MI | 1,787.49 mi (2,877 km) |
| I-95 | Miami, FL | Houlton, ME | 1,892.76 mi (3,046 km) |
Cool Facts About the Interstate System
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