How are interstate highways numbered
Roads and Railways
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One-and two-digit interstate highways are numbered according to their direction. Highways that run in an east-west direction are even numbered, while highways that run in a north-south direction are odd numbered. The lowest numbers are in the south and west, while higher numbers are in the north and east. For example, Interstate 10 is an east-west highway that runs from Santa Monica, california, to Jacksonville, Florida; thus, it has a even, low number. Interstate 95 is a north-south highway that runs from Houlton, Maine, to Miami, Florida; thus, it has an odd, high number. Three-digit interstate highways are short spur routes connected to a two-digit interstate.