The Beltway is notorious throughout most of Maryland and Virginia for horrendous traffic jams, high traffic volumes even when moving, and general unfriendliness to visitors. It is designated as Interstate 495 through its length, but its southeastern half also carries Interstate 95 around Washington.

One common problem to all beltways is how to designate directions -- if you're driving in a circle (actually, it's more approximately an oval), your direction will change N/E/W/S as you continue around the loop. The only consistent markings that can be used are Inner Loop and Outer Loop, designating which side is closer to or further from the center city. (For example, on the southern side of the city, eastbound lanes are the Outer Loop, and westbound are the Inner Loop; the situation is reversed on the northern side.)

River crossings are a major problem in the Washington area. The Woodrow Wilson Bridge on the southeastern side of the Beltway is old and decrepit, in addition to being a drawbridge and thus subject to a full stop whenever large ships must pass through; the American Legion Bridge to the northwest is simply way over capacity because of suburb-to-suburb commuting to the Dulles Toll Road (VA) and Interstate 270 (MD) technology corridors.

Here are all the interchanges on the beltway. As for the old exit numbers, the Maryland side was renumbered in 11-1979 (Prince Georges County, up to current exit 27) and 5-1980 (Montgomery County, north of current exit 27). The Virginia side was renumbered in 11-2000. The reason for the numbers in the 170s is that Interstate 95 uses the eastern half of the Beltway.

new old intersecting route
------- enters Maryland as I-95 north/I-495 north
  2  38 Interstate 295
  3  37 210
  4 37A 414
  7  36 5
  9  35 337
 11  34 4
 15  33 214
 16  -- USAir Arena
 17  32 202
 19  31 US Route 50
 20  30 450
 22  29 Baltimore-Washington Parkway
 23  28 201
 24  -- Park & Ride
 25  27 US 1
 --  26 Interstate 95
------- becomes I-495 west
 27  26 Interstate 95
 28  25 650
 29  24 193
 30  23 US 29
 31  21 97
 33  20 185
 34  19 355
 35  19 Interstate 270
 36  18 187
------- becomes I-495 south
 38  17 Interstate 270
 39  16 190
 40  16 Clara Barton Parkway
 41  15 Clara Barton Parkway
 43  14 George Washington Memorial Parkway
 44  13 193
 45  12 267 (Dulles Airport Access Road)
 46  11 123
 47  10 7
 49   9 Interstate 66
 50   8 US 50
 51   7 650
 52   6 236
 54   5 620
 57   4 Interstate 95/Interstate 395
------- becomes I-95 north/I-495 east
170   4 Interstate 95/Interstate 395
173   3 613
174  3A Eisenhower Ave
176   2 241
177   1 US 1

sources:
http://web.mit.edu/spui/www/boston/otherexitnumbers.html#i495va
http://web.mit.edu/spui/www/freeway/mdi495.html

Interstate 495 is a snake that’s constantly eating its own tail, shedding its miserable skin a mile at a time, trying to keep up with the demand for space, more space, more lanes. The existing concrete could support the volume of traffic if the drivers would realize they’re just one droplet in the river, but that’s not going to happen in D.C. The way we drive here, the construction won’t be done until the Beltway is eight lanes wide in each direction, three layers tall. Buses and compact cars on the bottom; wage slaves in the middle; an exorbitant monthly fee to drive your SUV on the top ring, to get a little more morning sunshine through your tinted windows. Everything here in D.C. is stratified and parceled out, and if you’re not at the top of the pile, in the front of the line – if you don’t get to pick the shiniest, sweetest apple in the barrel for yourself – you’re left out. You get the rotten windfalls. You have to beg for favors from the Anointed Ones. If you’re not the headline, if your name isn’t a buzzword, then the Washington Times will give you a few column inches on D6 to prove they still report on stories that the liberal media won’t touch with a ten foot pole, and by Wednesday, you’re nothing.

There’s not much room at the top, so it’s only natural that there’d be some anger, a few red faces, a blue word or six clouding the air inside the SUVs. All of the retired admirals remember how to curse like sailors as they drive to their revolving door contracting jobs. They still remember active duty: command is great, but the only command that matters is a carrier – the bigger the better. Subs are good too, but only the big ones, jam-packed with torpedoes longer than a man, tubes stuffed with Trident ICBMs, fractally phallic, a deterrent to other countries: mine’s the biggest. Long after the Beltway dwarfs the crisp ribbons of freeway through Los Angeles, there will still be construction here, still traffic jams, and it will still infuriate everyone who drives on it.

The NRO could use infrared photography from orbit to measure the increased average body temperature of a commuter passing through one of these construction zones on a weekday morning. The NSA could activate any of a thousand cell phones that trickle through a construction zone during rush hour -- and you know they can do it, even if your phone is off -- turn on your microphone and filter out the high staticky laughter of a wacky morning deejay, trim down the low tens-of-hertz rumble of the six liter V8 pulling the armor-plated station wagon that is the American SUV, use a notch filter to clip out the honking horns, and extract heart rates, violently accelerating as the owner’s car slows to a crawl around the Beltway, gobbling up following distance as if it were premium gasoline.

By 9:15, the Beltway’s work is done. Sneakers come off and high heels are strapped on pale, bony feet. Suit jackets are taken from hangers in the cavernous empty back seats. If you listen closely, you can hear the car alarms chirping in the packed parking garages like bats returning to their roost for the day, echoing up to street level. A hundred thousand white collars cling tight to sweaty purple necks. Every hurried decision made before lunch bears the taint of the Beltway commute.

At about 3:00 it warms up again and slowly turns on its axis, a stiff black concrete ribbon spinning with just enough wobble, all delicately balanced on the Capitol’s cupola. Now it’s hot outside, thick and humid because they built this city on a swamp. Or it’s raining, or snowing, or most likely some bizarre hybrid of the two guaranteed to make stop-and-go driving an exercise in aggression and humiliation. The friction grinds and grumbles as the flywheel slows down and grudgingly begins to swing back the way it came. The angular momentum generated is staggering; if we were just water in pipes, the sheer amount of heat generated by the stopping and starting would boil off some of the water. As it is, the cars boil off instead. An accident down by the Wilson Bridge, or up where I-270 competes with Escher’s prints for absurdity, will leave two or three hideously expensive cars piled up on the shoulder in an obscene coupling. Tired drivers make more mistakes, change lanes without signaling, sprint to get home because they deserve their free time more than you deserve yours. The commute home is a competition for leisure time, which they have earned, dammit, and which you obviously have not, you poor peasant. How dare you drive on their road? So many meals wolfed down in the evening rest in sour stomachs fouled by the almost audible malevolence of that road. This goes on for hours, sometimes as late as 7:00.

The construction crews never stop working. They sneak onto the road like white blood cells fighting infection in a sleeping body, taking advantage of the rest. They put up their bright night-work lights and sweat, unseen, into the early morning hours. It mixes with exhaust fumes and road grit, and settles like dew on the dark empty asphalt. Less than twelve hours later it starts up again.

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