With the exception of a few states which have signed roads using secondary compass points, such as northeast-to-southwest (and no state does so any longer), highways in the United States, as well as in Canada and Mexico, are usually signed with cardinal directions: north, east, south, and west. The designating authority decides that a road is best represented as north-south or east-west, and signs it accordingly. There are some cases in which a road is designated with both cardinal patterns along its length, but these are rare. Examples include US 62 from El Paso to Niagara Falls, which is generally an east-west road but is signed north-south in Pennsylvania and New York, and I-69 in Michigan, a north-south road that is signed east-west from Lansing to Port Huron.
When state representatives sat down in the mid-1920s to plot out the US highway system and post touring route numbers (like US 66) rather than names (like Lincoln Highway), it was decided that north-south routes would have odd numbers, while east-west routes would have even numbers. States were encouraged to implement this guideline, known as the rule of cardinal direction, on their own highway systems. Some states, such as Indiana, did so; others, such as New Jersey, did not. And even in systems that employ the rule of cardinal direction, spur highways often ignore it. For instance, US 122 (no longer assigned) was a spur from US 22, but it ran north-south and was signed as such. The Interstate highway system, established in 1956, employs the same general rules. Some routes, like I-26 and I-85, seem to ignore it, but even they are signed in accordance with their numbers.
While New Jersey’s main state highways do not follow the rule of cardinal direction, the 500 series of county highways does follow the rule, with a few exceptions. Some counties, such as Bergen, also implemented the rule, while many did not.