At first glance, high-rise Arlington doesn’t seem to permit denser development than DC. The “C-O-Rosslyn” zoning permits a Floor to Area Ratio (FAR) of 10 — equal to the C-4 zoning that covers much of downtown DC, 6th to 19th and Pennsylvania to Massachusetts. A segment along the north side of Pennsylvania, 10th to 15th, is actually zoned for 12 FAR, due to its special 160′ exemption under the Height Act. (This is one of many nonsensical bits within the Height Act; other streets in downtown, like L’Enfant Plaza and the Southwest Freeway, are just as wide and thus in theory present equal opportunities, but their property owners apparently aren’t as well connected as those fine hotels along Penn.)
Yet FAR in DC goes much further than that in Arlington. Along DC avenues, rights of ways typically extend all the way to the building line; front yards are often within the right of way. For example, in Woodley Park, Connecticut Avenue is just 60′ wide — but sits within a generous 130′ right-of-way, which gives it sidewalks ample enough for ambling and dining. Rosslyn, on the other hand, developed rather more haphazardly, and many of its wide roads were widened using easements onto private property.