neighborhood explorations: this view of density

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Definitions and Calculations

Residential Acre. Residential acreage excludes commercial, industrial, greenspace and agricultural land. If total acreage were used instead, a few dense residential units atop a sea of shopping and offices could appear to be low density sprawl. Compact development saves land for preservation as creeks, wildlife corridors and parks.

The following are typical densities:
0.1 Hh/Res Ac - Ranchettes.
1 Hh/Res Ac - Lowest density of single-family dwellings in sprawl.
3 Hh/Res Ac - Typical of single-family dwellings in sprawl.
10 Hh/Res Ac - Row houses with occasional single-family dwellings and apartment houses. Examples: lower density areas of larger cities, and older suburbs.
100 Hh/Res Ac - Mostly 3-5 story apartment houses with occasional mid- to high-rises and single-family dwellings. Examples: northeast San Francisco (Russian, Nob and Telegraph Hills, North Beach), River North in Chicago, Beacon Hill in Boston, along Connecticut Ave. in DC, and compact neighborhoods throughout the country.
500 Hh/Res Ac - Mostly mid- to high-rises. Examples: the Upper East and West Sides in Manhattan, and smaller neighborhoods in Chicago, San Francisco and elsewhere.

This calculator has been developed for densities ranging from sprawl, 3 hh/res ac, to 500.

Concrete or asphalt in roads and sidewalks. Paved surfaces create water pollution and require drilling, mining and transporting of gravel, cement and asphalt. Many studies show that water pollution skyrockets when more than 20% of the watershed is paved over and developed. Forty single family dwellings require 40 times as much concrete in roads and sidewalks as a 40-unit apartment building on a single lot. Water, sewer, electrical, phone, cable and other services lie under the street and branch off into each lot, so sprawl housing uses much more of these materials.

Extensive paving add to the "urban heat island" effect, worsening air pollution (NOx and hydrocarbons react to form ozone faster and more completely as temperature rises) and global warming.

Calculation assumes a 10 yard wide half-street and sidewalk along a 70 yard front for each 1 acre lot, or 700 sq. yards per residential acre.

Water Used. Water provision requires damming, transporting and loss of stream flow to fish and farms. In sprawl, most water is used on lawns and in washing cars, and it washes fertilizers, herbicides and pesticides off the lawns into streams, lakes and bays. Water consumption depends on the climate and other factors, but the calculator shows relative rates between compact and sprawl neighborhoods.

Calculations. Indoor. Kimberly Knox, SF Water Dept Water Cons (personal commun.): 55 g/p-d for multi-family units (~50 du/res ac). Assumes 80% is indoor use (44 g/p-d), and 3.8 persons per household.
Outdoor. Sakrison, "Water Use in Compact Communities: The Effect of New Urbanism, Growth Management and Conservation Measures on Residential Water Demands," Washington Dept of Ecology, 1998, Table 11 for 4, 7 and 12 du/ac, and extrapolated to higher and lower densities.

Shopping Opportunities. Neighborhood shopping enhances convenience, shortens trips, and reduces driving and traffic. Nearby work, shopping, education and recreation destinations shorten trips. But much zoning since 1940 prohibits markets and restaurants in residential areas, outlawing development of convenient communities.

Calculations are based upon data developed for the Location Efficient Mortgage‚ studies of the Chicago, Los Angeles and San Francisco regions by the Institute for Location Efficiency (Natural Resources Defense Council, Center for Neighborhood Technology and Surface Transportation Policy Project). The nearly 3000 neighborhoods are the Metropolitan Planning Agencies’ (CATS, SCAG and MTC, respectively) travel analysis zones, generally a census tract or two. This analysis applies to neighborhoods in metropolitan areas or within commuting distance of major job centers, not to isolated rural towns. Location efficiency lowers auto costs and can qualify you for a Location Efficient Mortgage‚.
Shopping = 0.1704 + 0.4814 Density. [R2 = 0.32]
Coding:
4 = little shopping nearby
40 = abundant shopping

Public Transportation. Increasing housing density and neighborhood convenience shortens trips. More people choose to walk, bike or take transit. So most public transit is provided to such convenient, pedestrian-rich areas. Of course, some otherwise convenient neighborhoods located off transit corridors might lack great service. Or, low density neighborhoods located near a subway stop might have great service. But, with these few exceptions, superior transit service is normally provided to compact, convenient neighborhoods.

A bus every 30 minutes becomes feasible above 7 hh/res ac, and every 10 minutes at 15 hh/res ac. Light rail service is feasible above 9 hh/res ac. Rapid transit is feasible above 12 hh/res ac. Public transit use increases fourfold as density increases from 7 to 30 hh/res acre.

Calculations are based upon data developed for the Location Efficient Mortgage‚ studies of the Chicago, Los Angeles and San Francisco regions by the Institute for Location Efficiency (Natural Resources Defense Council, Center for Neighborhood Technology and Surface Transportation Policy Project). The nearly 3000 neighborhoods are the Metropolitan Planning Agencies’ (CATS, SCAG and MTC, respectively) travel analysis zones, generally a census tract or two. This analysis applies to neighborhoods in metropolitan areas or within commuting distance of major job centers, not to isolated rural towns. Location efficiency lowers auto costs and can qualify you for a Location Efficient Mortgage‚.
Transit service = 2.6905 Density - 8.2799, but not below 0. [R2 = 0.30]
Coding:
5 = 2 nearby buses per hour, 1 each direction
50 = frequent bus service
200 = frequent bus and mass transit service

Vehicles. Their use requires mining, drilling, manufacture and transportation of materials and fuel. Inconvenient neighborhoods provide only one choice: driving and high vehicle ownership.

Calculations are based upon data developed for the Location Efficient Mortgage‚ studies of the Chicago, Los Angeles and San Francisco regions by the Institute for Location Efficiency (Natural Resources Defense Council, Center for Neighborhood Technology and Surface Transportation Policy Project). The nearly 3000 neighborhoods are the Metropolitan Planning Agencies’ (CATS, SCAG and MTC, respectively) travel analysis zones, generally a census tract or two. This analysis applies to neighborhoods in metropolitan areas or within commuting distance of major job centers, not to isolated rural towns. Location efficiency lowers auto costs and can qualify you for a Location Efficient Mortgage‚. If the actual public transit service, proximity to job centers and pedestrian friendliness are also known, better estimates of vehicles and VMT can be made using the detailed Location Efficient Mortgage‚ equations.
Vehicles/household = 2.4437 - 0.3749 Ln(Density). [R2 = 0.46]

Parking. More land for parking, less for nature. Each vehicle demands many parking places -- home, curbside, work, shopping, recreation. While it is difficult to identify and count the total mass of parking at home, work, shopping centers, curbside, parking garages and lots, etc., most estimates range from 5 to 9 spaces per car. The calculations are based on 7 parking places per vehicle.

Driving and Traffic. Traffic brings congestion, frustration and pollution. Convenient neighborhoods reduce vehicle miles traveled (VMT), give alternatives to driving (walking, biking, public transit) and shorten many driving trips. Other factors that are important to convenient neighborhoods, like nearby stores and restaurants, sidewalks and short streets, are absent in low density sprawl.

Calculations are based upon data developed for the Location Efficient Mortgage‚ studies of the Chicago, Los Angeles and San Francisco regions by the Institute for Location Efficiency (Natural Resources Defense Council, Center for Neighborhood Technology and Surface Transportation Policy Project). The nearly 3000 neighborhoods are the Metropolitan Planning Agencies’ (CATS, SCAG and MTC, respectively) travel analysis zones, generally a census tract or two. This analysis applies to neighborhoods in metropolitan areas or within commuting distance of major job centers, not to isolated rural towns. Location efficiency lowers auto costs and can qualify you for a Location Efficient Mortgage‚. If the actual public transit service, proximity to job centers and pedestrian friendliness are also known, better estimates of vehicles and VMT can be made using the Location Efficient Mortgage‚ equations.
VMT/household = 32237 Density-0.3135. [R2 = 0.54]

Gasoline. Its use requires drilling, refining, transporting and distributing. Increasing traffic and vehicle miles traveled increases gasoline consumption.

Auto Costs. Owning and driving vehicles is the second highest household expense, just behind the mortgage.

Calculations are based on calculated gasoline cost, plus other average 1999 operating costs (5.3 cents/mi) and ownership costs ($5534/yr) from AAA, Table 3-14, Average Cost of Owning and Operating an Automobile.

Air Pollution. Cars and trucks are the number one hazardous air polluter, according to the EPA. Cancer-causing and asthma-inducing pollutants include Volatile Organic Compounds, Nitrogen Oxides and Particulates, and CO2, the major greenhouse gas. Air pollution rains out as water pollution. Increasing VMT increases pollution.

Calculations are based on: 0.053 lb VOC /gallon, 0.13 lb NOx/gal, 28 lb CO2/gal and 0.012 lb PM10/mile (primarily reentrained road dust).