The Eisenhower Interstate System permits bypass and spur highway numbers to be recycled from state to state, so the most you can say about Interstate 495 without a further referrent is that it is supposedly a beltway forming a loop with Interstate 95 and allowing you to bypass a city or something else worth bypassing. By its very nature, 495 is going to be one of the more significant roads to people trying to go any distance in the vicinity of one, so each has its own distinct character that locals will merrily natter on about. There are five instances of the class Interstate 495 in six states at present, at least according to the inimitable Federal Highway System Route Log at http://www.fhwa.dot.gov/reports/routefinder/ and the AARoads guide at http://www.aaroads.com/interstate/:
- 495 in Maine used to be the Maine Turnpike, connecting Portland and Gardiner via Lewiston over a distance of 50.47 miles. Legislation passed in 2001 and implemented in 2002 rerouted 95 over the Turnpike, made the old 95 part of 295, and reduced 495 to a small segment connecting the two other roads between Portland and Falmouth.
- My 495 is the outer circumferential highway around Boston—the inner loop being Route 128/Interstate 95 itself. The second-longest three-digit interstate in the system after Interstate 476, it runs from Newburyport down to Wareham by way of (for brevity, restricting it to places I have actually heard of before researching this node) Haverhill, Lawrence, Lowell, Hopkinton, Bridgewater and Franklin for a total of 121.56 miles.
- 495 in New York is the Long Island Expressway, "the backbone of Long Island". Political maneuvering gave it a three-digit interstate designation with an even first digit despite the fact that it is neither a loop nor connected directly to Interstate 95. Its 66.38 miles of asphalt connect Queens to, well, Long Island, by way of Long Island. Essentially a sop to the upwardly mobile sorts who can afford to drive into Manhattan but not to live in it; everyone else takes the train.
- Delaware's 495 connects Newport and Delaware while wisely skirting Wilmington. If Delaware actually existed, this highway would be 11.47 miles long, the shortest 495 of the bunch.
- The southernmost 495 is the world-famous Capital Beltway, straddling Maryland and Virginia over 31.41 miles in a desperate and ultimately futile attempt to keep D.C. from leaking out and discomfiting the rest of us. Besides the occasional Stephenson-esque skirmish among rival spy agencies and less organized local gangs, it's mostly just a parking lot for bureaucrats, diplomats, and those who man the various industries built to manipulate, serve, and snoop on them.