Not too long ago, Bloomberg Citylab featured my maps of intersections in US metro areas. Their article didn’t embrace maps of the Washington area, so right here’s a comparability of intersections in several components of our space.
Why intersection sorts matter
Road networks are an vital a part of city type, each for pedestrians and for public transit. In historically gridded cities, like New York, an everyday sample of lengthy, straight roads offers pure routes for buses and good connectivity for pedestrians to get the place they’re going with out taking oblique routes. When three-way intersections predominate, buses typically need to observe winding, oblique routings to serve communities — for instance the A22 in Prince George’s County — or many routes overlap on the small variety of straight via streets, reminiscent of Rte 7 and US-1 in Northern Virginia.
Suburban areas constructed after World Struggle II, then again, are inclined to have curving streets that hardly ever meet at four-way intersections, and still have such a lot of cul-de-sacs that DC-area cartoonist Richard Thompson’s nationally-syndicated cartoon about suburban life was referred to as Cul de Sac.
This alteration in road networks was a consequence of Federal coverage: the Federal Housing Administration, established through the New Deal to underwrite loans for the development of recent residential subdivisions, promoted residential areas made up of “neighborhood units” that discouraged via site visitors by not having full grids. Then, in 1965, the Institute of Transportation Engineers printed suggestions that subdivisions ought to keep away from four-way intersections and will use cul-de-sacs and curving streets with solely three-way intersections to gradual site visitors.
Right now, many native governments are attempting to encourage a return to better-connected road networks with few dead-ends and extra four-way intersections. For instance, Fairfax County is encouraging better connectivity in Tysons and Prince George’s County rules now require new developments to connect their inside highway networks to neighboring areas higher. Nevertheless, it may be an uphill climb. In addition to the apparent difficulties of retrofitting present road networks so as to add connections, residents in lots of areas are still pushing to have intersections closed to cut back site visitors of their neighborhoods.
Intersections in DC and the suburbs
A take a look at the intersections contained in the Beltway exhibits that the city core of the DC area doesn’t a lot have one rectilinear road grid as a number of of them. Within the unique L’Enfant core of the town — the world bounded by the Potomac, the Anacostia, Rock Creek, and Florida Avenue — most intersections are four-way, although clusters of three-way intersections might be seen at circles, alongside Ok Road (as a result of the OpenStreetMap highway community knowledge I used treats the service lanes as separate roads), and the place main avenues reduce throughout the road grid.
Some areas of the District outdoors the L’Enfant core, which largely developed as streetcar suburbs within the late nineteenth and early twentieth centuries, even have their very own road grids, however they aren’t nicely linked to one another. The biggest of those, north of Florida Avenue and bounded to the west by Rock Creek Park and the east by the Previous Troopers’ House and Rock Creek Cemetery, offers an everyday road community alongside among the area’s busiest bus routes on sixteenth Road and Georgia Avenue.
The Brookland-Langdon space alongside Rhode Island and Michigan Avenues is the most important space with an everyday road grid in Northeast, however it’s largely separated from different areas with linked road networks by New York Avenue and the institutional land makes use of alongside North Capitol Road and the Metropolitan Department. West of Rock Creek, Chevy Chase, Friendship Heights, and Tenleytown type the same space, separated by Rock Creek and different stream valleys from a lot of the L’Enfant Metropolis.
East of the Anacostia River, we do see grids of four-way intersections alongside East Capitol Road and in historic Anacostia, however a lot of the world is way more broken-up into post-Struggle-style road networks.
Lastly, Georgetown — which, together with Previous City Alexandria — had a street grid predating the establishment of the District and the town of Washington is seen as a comparatively remoted part of closely-spaced four-way intersections, with three-way intersections seen alongside Wisconsin Avenue.
Wanting north, to Montgomery County, we see a particular gradient. Contained in the Beltway, and simply north of Veirs Mill Highway, we see areas with road networks that largely encompass four-way intersections, stitched collectively by areas the place three-way intersections dominate. Additional north, although, cul-de-sacs turn into at the least as widespread as three-way intersections, particularly within the Gaithersburg space.
Prince George’s County has a a lot much less linked road community on a big scale: even contained in the Beltway, there are boundaries, reminiscent of Kenilworth Highway, the Baltimore-Washington Parkway, US-50, Central Avenue, and Suitland Parkway which have only a few connections throughout them. Conventional rectilinear road networks are most seen within the a number of streetcar suburbs within the Route One hall working as far north as Beltsville: this space was residence to the county’s only long-lived streetcar line. Various small gridded areas are seen alongside the Northeast Corridor rail line and alongside the previous Baltimore, Washington, & Annapolis interurban line.
A very noticeable plan might be seen within the parts of Bowie that have been a part of the Levitt and Sons’ “Belair at Bowie” subdivisions constructed round 1960. This space has unusually closely-spaced intersections for Prince George’s County outdoors the Beltway, and it is vitally notable that they’re practically all three-way intersections: each cul-de-sacs and four-way intersections are very uncommon.
A number of areas of Arlington County and Alexandria appear to have comparatively gridded road networks, together with Previous City Alexandria, in fact, but in addition Del Ray, Aurora Highlands, and the Ballston-Rosslyn hall.
The Northern Virginia suburbs are extra densely crammed with intersections outdoors the Beltway than the Maryland ones are, although — as normal — the Difficult Run valley is a notably sparse space. Cul-de-sacs appear to be considerably extra widespread than they’re in Maryland, although, with important numbers of them even contained in the Beltway.
Intersections in Baltimore and Richmond
Increasing our view to incorporate different close by metro areas exhibits that Baltimore and Richmond look a bit totally different from Washington, with extra constant rings of road community sorts: gridded areas within the heart, mixtures of three and four-way intersections additional out, and at last a belt of cul-de-sac nation.
Baltimore’s core space of tightly-spaced, gridded streets is comparable in dimension to the L’Enfant Metropolis, which isn’t actually stunning in gentle of the statement that pre-streetcar cities hardly ever grew greater than three miles throughout, since few individuals have been keen to commute greater than a couple of mile and a half — a thirty-minute stroll — to get to work.
Richmond’s densely-gridded core is a bit smaller however, as in Baltimore, it’s surrounded by less-dense areas with extra three-way intersections that seemingly had their origins as streetcar suburbs. Neither metropolis, nevertheless, has the numerous satellite tv for pc grids that our area has.
Comparability to cities outdoors our area
It could come as no shock that New York’s road community is exclusive within the nation. Not a lot for having common grids as within the dimension of the world coated by densely city grids: not solely Manhattan however practically all of Brooklyn and far of Queens and the Bronx as nicely. Nonetheless, the particularly-dense community in decrease Manhattan — which developed as a standard pedestrian metropolis earlier than the Manhattan road grid was plotted out in 1811 — stands out from the larger-blocked grids within the parts of the town that developed later alongside streetcar, elevated, and at last subway strains.
However, the Boston space — which has practically the identical urban area population as Washington in response to the Census — has far fewer four-way intersections than our area. This doesn’t imply that the world’s road networks aren’t well-connected: a lot of the area developed as streetcar suburbs, however with three-way reasonably than four-way intersections because the norm.
It’s notable, nevertheless, that the areas with probably the most common rectilinear grids, reminiscent of South Boston and the Again Bay have been constructed on landfill within the nineteenth Century, whereas the outdated pedestrian-city core of Boston, which is notoriously ungridded, is essentially made up of three-way intersections.
Atlanta, one other metropolis with a really related city space inhabitants to Washington, however with a way more car-oriented and unwalkable city type, exhibits that intersection density can matter as a lot because the varieties of intersections. Atlanta has bigger areas of primarily four-way intersections than Boston however, apart from a small core in downtown, few areas with many densely spaced intersections. Moreover, as quickly as one leaves Atlanta correct, cul-de-sacs appear to turn into practically as widespread as intersections of any sort.
These variations in road grids might be extra persistent than density patterns, as a result of highway networks, as soon as constructed out, are so hardly ever modified, whilst inhabitants and employers transfer in or out of an space. This makes it notably vital that new developments be constructed with walkable, transit-friendly grids.
On the identical time, the standard — or repairability — of the road grid must be taken under consideration in plans to densify areas and enhance their transit. Areas with low density, however robust road grids, such because the portion of Northwest west of Rock Creek Park are notably interesting areas for elevated densification.