The logic behind road numbers

From Willipedia

(The word "road" is used here to avoid the route/highway argument.)

Knowing the logic behind road numbers can help you navigate when you are lost.

Roads that circumscribe major metropolitan areas have three digits. Thus, 495 circumscribes the Boston area. The last two digits names (at least one of) the interstate(s) that this road stems from and connects to.

Furthermore, three-digit interstates with a even first digit are ring roads that run around cities, like 495. Odd first digits (like 395 in CT) signify a spur highway to a city.

Roads that run north/south have odd numbers and roads that run east/west have even numbers. Thus, 95 runs from Florida to Canada, and Route 66 is perhaps the most famous example of an American east/west road. There are some caveats to this, however. Local parts of a north/south route may run east/west for relatively short spans, and vice versa. Even though Route 1 in Pennsylvania and New Jersey, for example, is odd numbered, long stretches of it travel farther east/west than north/south.

It also helps to know that the numbers for interstate highways mostly increase from west to east and south to north.

Knowing this logic can (sort of) help you navigate when you are lost.