Environmental Characteristics of Smart Growth Neighborhoods
An Exploratory Case Study
No definitive conclusions can be reached from a single exploratory case study. However, the study found enough significant differences in the built environments and travel characteristics of the Sacramento sites to suggest that the design and location features associated with smart growth and new urbanism may enjoy notable environmental advantages under certain circumstances. The type and magnitude of advantages found in Sacramento are consistent with those found in previous EPA studies of proposed infill versus greenfield development in San Diego, Atlanta, Montgomery County, Maryland, and Palm Beach County, Florida (see Impacts of Infill vs. Greenfield Development, EPA 231-R-99-005, 1999; and Project XL and Atlantic Steel, EPA 231-R-99-004, 1999).
Although the Sacramento findings cannot by themselves justify broad conclusions about the impacts of design elsewhere, it appears that Metro Square residents create fewer negative environmental impacts than Natomas or Antelope households as follows:
- Metro Square households occupy about one-quarter of the land area that their suburban counterparts use.
- Metro Square's construction required no conversion of productive resource land, whereas productive agricultural land was permanently lost at both suburban sites.
- Metro Square households use about 20-30 percent less water than their suburban counterparts because of smaller yards, and more rainfall and other surface water is returned to ground aquifers at Metro Square because of its smaller amount of impervious surface per capita.
- Metro Square residents enjoy a much richer mix of neighborhood services and amenities within walking distance, along with more inviting pedestrian features, and thus appear to take a far greater proportion of their trips by foot than do their suburban counterparts. They also appear to take fewer motor vehicle trips per person and, based on the most recent regional travel data, likely drive far fewer miles per person. As a result, it is likely that Metro Square residents consume as little as half as much fuel and emit as little as half as much pollution and greenhouse gas as their counterparts in Antelope and Natomas.
- Metro Square's construction required no new infrastructure of any kind, whereas the suburban sites required a full complement of water, sewer, streets, drainage, and other improvements that represent enormous amounts of embodied energy and upstream pollutant emissions.
These and related findings are discussed below according to the built environments and travel demands of the three sites.
As shown in Table 4, Metro Square's built environment scored better than Natomas and Antelope on all indicators except sidewalk presence, which was 100 percent in all cases. (Metro Square's sidewalks are, however, wider than those in Natomas and Antelope.) Compared to the conventional developments, Metro Square uses much less land, in a location much closer to jobs and amenities, with superior access to multi-modal transportation systems. Metro Square's design is considerably friendlier to pedestrians and bicyclists, and its neighborhood possesses a mix of destinations appropriate to those modes. This may help account for the substantial increase in walking reported by Metro Square residents in comparison to their previous addresses as well as in comparison to Natomas and Antelope. Notable results for specific built environment indicators include:
- Density. Metro Square's homes are built at a density of 20 dwelling units/acre (DU/ac) versus 6-7 DU/ac at Natomas and Antelope. The former is a highly supportive density for frequent transit service, while the latter falls at what most experts consider a bare minimum for infrequent transit service. The Metro Square design is notable for achieving such a relatively high density while still retaining detached single-family structures that have wider market appeal than attached housing. Indeed, according to the developer all of Metro Square's homes were contracted for sale within one day of their first offering.
- Diversity. Due to the richness of its urban setting, Metro Square has a diversity of nearby services and amenities unmatched by Natomas and Antelope in their single-use suburban settings. In terms of neighborhood completeness, the percent of specific key uses within one-quarter mile is 72 percent for Metro Square versus 5 percent for the suburban sites. On a broad spatial basis, generalized use mix in the vicinity of Metro Square is more than double that of the other sites. The high level of diversity at Metro Square translates into significantly shorter travel distances to key destinations such as the closest transit stop, elementary school, grocery store, and park. Metro Square's superior diversity is also apparent in the 30,000 jobs that exist within one mile versus none at Natomas and only 35 at Antelope.
- Circulation. Metro Square's location in a traditional grid-style neighborhood of small blocks gives it significantly better physical characteristics for multi-modal circulation. Metro Square's streets have higher connectivity for more convenient and direct travel, and the site is much more permeable for ingress/egress by all modes. Metro Square provides a more pedestrian-friendly environment, with wider sidewalks, shorter street crossing distances, and more extensive traffic calming and control devices. Bicyclists also enjoy considerably greater attention in terms of more dedicated routes and better inter-neighborhood connections.
- Environmental design. Metro Square's high-density design enabled 10 percent of its land area to be retained as common open space compared to 2 percent at Natomas and none at Antelope. Metro Square also created about 10 percent less impervious surface per capita than Natomas and Antelope. These features translate into less water consumption for irrigation in Metro Square's smaller yards, and better aquifer recharge from rainfall and other surface water at Metro Square due to more permeable surface per capita.
Metro Square Travel Compared to 1991 Antelope Conditions
The Antelope travel data are based on a regionwide household survey conducted in 1991. Care must be taken when comparing these data with recent survey results from Metro Square since the regional survey, based on detailed travel diaries, was more sophisticated and rigorous than the questionnaire given to residents of Metro Square. In addition, travel characteristics may have changed since the 1991 survey. For instance, between 1991 and 1998 per capita miles driven in Sacramento County rose by roughly 5 percent, indicating a general increase in people's propensity to drive and/or an increase in average distance driven per trip. In addition, given that households at Metro Square are somewhat smaller than the regional average, per capita comparisons will often be more meaningful than household comparisons.
Notwithstanding these limitations, the data from this study and from the regional survey indicate a number of travel-behavior characteristics of Antelope and Metro Square that may be environmentally important. First, reflecting the relative lack of destinations within walking distance of Antelope, its per capita automobile trip rate is significantly higher than the regional average calculated from Table 5. By contrast, the per capita auto trip rate appears significantly lower for Metro Square. While the travel diaries and the survey-based results are not directly comparable, it is likely that a significant amount of the indicated difference is real given the size of the indicated disparity.
Almost certainly real is an apparent difference in per capita miles driven between the two developments. In the 1991 regional travel survey, residents of the travel analysis zone (TAZ) that now includes Metro Square were found to drive only 57 percent as many miles per day as did residents of the TAZ for Antelope.
While the Metro Square development was not yet built and occupied at the time of the survey, such a difference would be expected, given the much greater proximity of typical travel destinations to Metro Square's more central location.
As noted, there is evidence that residents of the region as a whole drive somewhat farther per day now than they did in 1991. However, there is no reason to suspect that this increase would cause the apparent difference between the two locations in miles driven to shrink. Indeed, given that increases in driving distances tend to be particularly manifest in the suburbs, the difference today may be even greater than that suggested by the 1991 data.
A work trip mode split comparison between Metro Square and Antelope shows some interesting differences. Antelope commuters tend to drive alone to work a bit more frequently than Metro Square residents, as would be expected given their respective locations. However, carpooling among Antelope and Metro Square residents is almost identical. One might generally expect that travelers from suburban locations with longer travel distances would be 7more likely to form carpools than residents of central, urban neighborhoods, but that does not appear to be the case in this comparison.
In addition, no Antelope residents report walking to work, reflecting the lack of land use diversity and the large distances between destinations in that location. There is also no reported usage of public transit for work trip purposes in Antelope. Metro Square residents reported some usage of both transit and walking as work trip modes. As for non-work trips, the estimates of mode split for Metro Square were derived only from the destinations specified in the residents' survey questionnaire, and so are not entirely comparable with the diary-based estimates from the Antelope area. However, Metro Square residents report a much stronger tendency to walk to non-work destinations than their counterparts in Antelope. Again, given the size of the suggested disparity between the two locations, it is likely that a significant degree of difference is real. The average auto ownership in Antelope is consistent with the regional average for households of that size, as is Metro Square's auto ownership.
Metro Square Travel Compared to Regional Averages
Metro Square residents take an average of 2.8 automobile trips per capita per day, significantly less than the 3.9 trips per day taken by the average resident of the region as a whole. However, as noted elsewhere, the Metro Square auto trip rate is based on estimates by residents rather than detailed travel diaries, as were used in the regional survey. Because, unless diaries are used, survey respondents may forget some of their trips, this phenomenon may be responsible for some of the apparent differences between Metro Square and the regional diary-based trip statistics. Nevertheless, the reported difference is a large one and may be significant.
The apparent difference between Metro Square and the regional average with respect to per capita driving distance per day is pronounced. Residents of the TAZ that now includes Metro Square were found to drive only half as many miles per day as the average resident of the Sacramento region. As noted above, this is likely due to the richer mix of services and amenities in and around Metro Square's TAZ. Even when residents of the neighborhood drive, they need not drive far.
The means by which Metro Square residents travel to work also differ from the regional averages. For instance, the rate of carpooling among Metro Square residents is lower than the region as a whole. However, Metro Square residents report that their travel time and distance to work has decreased substantially since moving to the neighborhood. A relatively small amount of ride-sharing is, therefore, to be expected. From the traveler's perspective, the benefits of carpooling are smaller for short trips than long trips. This is because the shorter line-haul travel time makes the extra time spent picking up passengers a greater share of the total time devoted to travel.
As suggested by the lower carpooling rate, residents of Metro Square tend to travel to work by driving alone more frequently than residents of the Sacramento region as a whole (83 percent versus 76 percent). However, given the increase in per capita VMT that has occurred in the past few years, it may be that current regional mode split statistics would show higher levels of drive-alone work trips than the 1991 survey upon which the regional average was based, thus shrinking the difference between Metro Square and the regional average. In addition, for commuting trips, Metro Square resident mode choice will continue to be influenced by characteristics related to the workplace end of the trip, including the availability of free parking and low-congestion reverse commute driving conditions. Metro Square is centrally located with excellent freeway access; this good regional accessibility combined with relatively short travel distances may make travel by transit or other modes less competitive with the automobile. This also could account for the higher drive-alone mode split percentages. Finally, the continuing tendency to commute by driving may be partially due to the fact that Metro Square was a very new neighborhood when this survey was conducted, and residents may not have had time to adjust their routine travel patterns in response to their new location.
The estimates of non-work mode split for Metro Square residents were derived only for the specific non-work trip destinations requested in the survey, and so are not entirely comparable with the travel diary-based estimates that make up the regional averages. Nevertheless, Metro Square residents report a very strong tendency to walk to a number of non-work destinations, reflecting their neighborhood's proximity to personal and household services and civic facilities.
The per capita vehicle ownership rate at Metro Square is higher than the regional average (0.94 vehicles per person versus 0.72 regionwide). However, the average household in the development is somewhat smaller than the average. Vehicle ownership rates in Metro Square are no different than the typical regional values for households of this size.
Metro Square Resident Travel Compared to Previous Address
While a few Metro Square residents moved to Metro Square from other central Sacramento locations, a number of the residents previously lived in typical suburban locations such as Folsom and Citrus Heights (see Figure B-1). These residents may have chosen Metro Square because it offered a neighborhood lifestyle that appeals to them, while also being closer to their jobs, local services, and cultural opportunities. Overall, Metro Square residents seem satisfied with their location choice; at least 70 percent rate Metro Square as the same as or better than their previous neighborhood on several measures of neighborhood quality.
Metro Square's proximity to basic household services (e.g., dry cleaners, video stores, parks) is reflected in the substantial increases in walking to these types of destinations reported by Metro Square residents, when compared to their previous addresses. Metro Square residents report that they are now far less likely to drive to non-work destinations than they were before moving to the neighborhood. The proportion of Metro Square residents driving to work is slightly lower than at their previous residence locations, and the proportion of residents commuting by carpool has increased substantially. It is clear that the typical distance between home and work is significantly shorter from Metro Square. In fact, residents report that travel distances for all types of trips decreased substantially after moving to Metro Square.
Almost all Metro Square residents report making the same number or fewer motorized trips during a typical day than they did at their previous addresses. Eighty-eight percent say they make more walking and bicycling trips since coming to Metro Square, and most indicate that there is some practical component to those trips (i.e., they are not strictly for recreational purposes). This indicates that Metro Square residents enjoy equal or greater access to services and amenities than they did in their previous locations, while relying less on motorized forms of transportation.
The Issue of Self-Selection
The information relating to residents' behavior at their previous locations bears on the issue of self-selection: that is, the possibility that any differences observed between Metro Square residents and the regional averages may not be attributable to characteristics of Metro Square, but rather to inherent preferences among the people who choose to live in Metro Square. At their previous addresses, Metro Square residents were indeed more likely to walk, bike or ride transit than the regional average. This indicates that self-selection may be responsible for part of the difference between Metro Square residents and others in the region. However, since moving to Metro Square, their mode split characteristics have generally improved. Particularly for non-work trips, Metro Square residents now walk much more and drive less than they did at their previous residence location. This suggests that their current residence in Metro Square does make a difference. Moreover, it must be noted that, to the extent that Metro Square residents may be self-selected, such developments facilitate a positive phenomenon: they provide those who would like to travel by multiple modes an increased opportunity to do so. The very strong sales performance of Metro Square homes indicates that the demand for neighborhoods that facilitate such lifestyle preferences is great.
Returning to the original list of relevant environmental issues, the study found the following principal conditions among the three sites:
|Environmental Issue||Metro Square vs. Natomas & Antelope|
|Land consumption||In both absolute and per capita terms, Metro Square consumed roughly one-quarter of the land that Natomas and Antelope consumed.|
|Resource land conversion||100% of Natomas and Antelope were previously agricultural land whereas the Metro Square property had no natural resource values.|
|Open space preservation||Metro Square's new urbanist design enabled five times more public open space preservation on-site than the conventional layouts of Natomas and Antelope.|
|Water consumption||This could not be precisely quantified because the City of Sacramento does not meter water use. However, given that Natomas and Antelope yards are approximately six times larger than those of Metro Square, it is reasonable to expect proportionately less irrigation consumption by Metro Square households.|
|Stormwater runoff||Metro Square's smaller amount of impervious surface per capita suggests reduced runoff (and reduced impediments to groundwater recharge).|
|Construction-embodied energy use||Metro Square required no new municipal infrastructure whereas Natomas and Antelope both required entirely new streets, water, sewer, and storm drains, all of which required large amounts of energy use (and emitted air pollution associated with that energy use and its production) during construction.|
|Travel energy use, air pollution and greenhouse gas emissions||Not precisely quantifiable under the design limitations of the exploratory study. But the evidence suggests that Metro Square residents walk more and drive less than their counterparts in Natomas and Antelope, with rates of fuel consumption and emissions as much as 50% lower than Natomas and Antelope.|
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Kaid Benfield writes about development, community and the environment on Switchboard.
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