In a time of rapid urban growth, how our cities grow matters. This report focuses on how suburbs have been built in the past, how existing urban areas perform in the present, and how future urban areas might be built to achieve policy objectives. Although many of the approaches and findings in this study are relevant to other jurisdictions, this project originated in response to Toronto-region policies and conditions, some long-standing, others new. Of particular importance is the 2006 Growth Plan for the Greater Golden Horseshoe. In part, the plan seeks to reduce automobile dependence, promote more efficient provision and use of infrastructure, and decrease the rate of conversion of rural land to urban uses. For future development on greenfield land, the plan's policies promote the creation of "complete communities" -- urban form and activities that are more mixed, dense, and conducive to travel by means other than the automobile relative to currently prevailing forms. To support these policies, the provincial government has set a minimum density target of 50 residents and jobs combined per hectare for the designated zones of future greenfield development of single- and upper-tier municipalities.

Analysis of existing urban areas

This report examines 16 districts from all of the regional municipalities in the Greater Toronto Area and from the City of Toronto, each of which represents a different combination of physical and demographic attributes. The 16 study areas each cover about 400 hectares. Densities were calculated for the 16 study areas, and these measurements, along with information on each area's urban form, demographics, and travel patterns, were used to determine the factors that influence the density of an area and the way in which density affects the way an area functions and how people use the area. The findings are grouped in six topic areas.

1. Density and era of development. Dwelling unit density is lower the more recently a study area was developed. Population density, however, does not follow the same trend because, on average, household size is higher in more recently built areas (largely because dwellings are larger in these areas). Reports that densities in neotraditional developments from the late 1990s are higher than those in conventionally planned subdivisions of the 1960s and 1970s are not borne out in this study. All of the study areas developed after 1980 have combined population and employment densities of less than the Growth Plan's target of 50 residents and jobs combined per hectare, calculated on either the full land base (gross area) or the developable land base (the gross area minus areas unsuitable for development).

2. Density and changing standards for public facilities. The proportions of both gross and developable land area accounted for by public facilities vs. private property vary little across the 16 cases. When different types of public facilities are considered separately, however, the proportions for parks, schools, and roads exhibit no trend by era of development. On a per-capita basis, parkland area is higher the more recently an area was built. There is no pattern for schoolyard area per capita.

3. Density and housing type mix. In general, fewer single-detached houses and more apartments as a proportion of all dwellings in a study area result in higher net residential densities. The proportion of detached dwellings in the housing type mix is the most significant determinant of net residential dwelling unit density. The proportion of apartments and duplexes in the housing type mix is only loosely associated with higher net residential density. The effects of housing type mix on population density are mediated by average household size: larger average household size amplifies the impact of housing type mix on population density; smaller average household size diminishes it.

4. Street configuration and neighbourhood accessibility. Different street and block configurations are associated with different eras of development. As planning techniques changed in the postwar period, so too did the way street systems in new suburbs were laid out. Prewar study areas feature uniform grids and little differentiation between "major" and "minor" streets. Postwar street networks were designed to channel through-traffic along major arterial roads and discourage high volumes of traffic in minor streets between them. These internal street networks tend to feature cul-de-sacs and be discontinuous, curvilinear, and disconnected from bordering arterial roads. As a result, postwar neighbourhoods are expected to be less easily traversable on foot or by bicycle.

5. Employment, segregation of land uses, and jobs-housing balance. The pre-1960 study areas feature small-format retail and services on pedestrian-oriented streets. More recently developed study areas contain fewer jobs, most of which are in business or industrial parks or in large-format retail centres and are distributed on a larger scale than the 400-hectare study area can capture. Given the low number of jobs compared to the residential population in most study areas, and the lack of employment land in areas built after 1960, the potential for neighbourhood self-containment (that is, a population that lives and works in the same area) in these areas is low. Moreover, without large-scale redevelopment, the lack of employment parcels will likely restrict the growth of employment in residential areas.

6. Travel behaviour. The combined mode share of automobile, taxi, and motorcycle for journeys to work and shopping is high in all study areas. Only journeys to school and childcare show a higher mode share for walking and cycling than for the automobile, although this is not the case in areas developed in the 1980s and 1990s. In general, densities tend be higher and automobile use lower the closer the area is to Toronto's central business district. The relatively high transit mode share in the City of Toronto study areas is no doubt a function of the integrated and frequent service offered by the Toronto Transit Commission. No definitive relationship was found between a more connected street layout and mode share.

Exploring development scenarios

The study includes an analysis of the effect on density of hypothetical development scenarios. This part of the study used an activity-optimizing model, in which the objective is to determine the optimal capacity of a fixed quantity of land -- i.e., how many people, jobs, and associated uses it could accommodate within typical constraints on land use.

Eight scenarios were tested. The baseline scenario represents the densities likely to occur under prevailing assumptions about future patterns of growth. The seven alternative scenarios provide a sense of how much might be accomplished through the adjustment of four variables: housing type mix, standards for public facilities, standards for natural heritage protection, and the location and density of employment. Each scenario was applied to three hypothetical pieces of land, each representing a different degree of natural heritage protection. The results of this exercise led to the following three findings:

1. Shifting the housing type mix to higher-density dwellings while reducing public facilities standards can increase overall density, although the latter change may have a larger impact.

2. The more land allocated to natural heritage protection, the lower the gross density. Removing land from urban development for environmental protection must be balanced against the need to create contiguous urban form that supports walkability, the effective provision of transit, and other objectives.

3. Greater intermixture of residential and non-residential uses reduces density at the local-area scale, because jobs density is usually lower than population density. The creation of more mixed and more "complete" communities at the secondary plan scale may therefore reduce local-area densities below levels needed to support high-frequency public transit.

Implications for policy development

1. Density should be supplemented by other measures in planning practice. In -general, density is a commonly used measurement in land use planning because it can be simple to calculate and is expressed in numbers that can be used for land use regulation. However, the prescriptive use of density numbers alone with the expectation that certain outcomes will occur may prove ineffective, because density captures neither the full range of variables that make up urban form, nor the complex relationships between them.

While density is a useful indicator of the efficiency of infrastructure and service provision, especially for public transit, it tells us little or nothing about other important attributes of urban form: housing type mix, the degree to which uses are mixed, contiguity of the urbanized area, and the connectivity of street systems. Also, combining population and employment densities obscures the balance between the two, and therefore is a poor indicator of the degree of mix of use. Finally, setting density targets for large areas may be ineffective in boosting densities in specific nodes and corridors to levels high enough to support transit.

In light of this, the Growth Plan's policies might be better supported if, in addition to the municipality-wide minimum density target for designated greenfield areas, the Province were to establish a minimum density target for individual subdivisions, as is done in parts of the U.K.; separately monitor and regulate segregated employment zones (business, industrial, and retail parks); measure and monitor the degree of contiguity of the urbanized land base, mix of use, and neighbourhood accessibility; and comprehensively assess the degree to which protecting natural heritage features and systems decreases the overall contiguity and density of urban areas.

2. An already changing housing type mix is likely to deliver higher densities. The smaller lot sizes that accompany the move from detached to attached housing appear to be more decisive in producing higher densities than increasing the proportion of apartments, although all study areas with a net residential density of over 30 units per hectare had a housing type mix in which apartments accounted for more than 30% of the mix. If the production of single-detached housing as a proportion of total housing construction decreases, as it is forecast to do, densities will increase.

3. The changing composition of households may affect the viability of services. The ongoing decline in household size may, over time, reduce the efficiency of infrastructure investment and service provision, and undermine the cost-effective provision of public transit. One response is to encourage flexible building types and urban forms that permit adaptation to different potential futures.

4. Greater mix of use may actually reduce densities at the local level. Since jobs density on employment lands tends to be lower than the population density of residential areas, redistributing land uses at the metropolitan regional scale to promote greater local-area mix of use may frustrate the goal of increasing local area densities.

5. Smaller and smarter allocations for public facilities would increase densities. Careful planning of public facilities could increase density by expanding the amount of land available for private residential and commercial development. The options include planning dual-use park and schoolyard facilities, locating playing fields on flood plains, and integrating parks into protected natural heritage systems.

6. While meeting the Growth Plan's minimum density target is feasible, the promise of "complete communities" will be less easily fulfilled. Even if there were enough employment land in a particular area to support one job for every member of the resident labour force of that area, there is no guarantee that residents would work locally. People may prefer to work, shop, and use amenities in neighbourhoods other than their own. Attempts to alter urban form are likely to have an incremental rather than transformative impact on travel behaviour.

7. Existing postwar suburban areas will be hard to retrofit. Street networks change very little over time, if at all. Segregated land use patterns are also not easily reversed. While site-by-site redevelopment may bring additional jobs and people into an established urban fabric, a generalized increase in local-area mix of use and density would take decades. Meanwhile, intensification must offset the effects of declining average household size before a net increase in population and jobs occurs.

Over time, we may see a dense metropolitan core surrounded by lower-density suburbs, which is in turn surrounded by a newer, higher-density band of development built according to newer standards. The challenge of how to raise the performance of the middle band and efficiently connect the three urban realms by transit is formidable.

8. Change will take time. It will be years before the Growth Plan produces demonstrable change. While all development applications had to conform to the plan after its enactment, municipalities have until June 2009 to bring their official plans into conformity. It will probably be several years into the next decade before the Growth Plan's policies are reflected in the full hierarchy of planning documents: from upper- and lower-tier municipal official plans to secondary plans and zoning bylaws. It will be later still before a visible portion of the built environment reflects the impact of the Growth Plan. Indeed, there are tens of thousands of dwellings "in the pipeline" -- planned and approved under previous rules -- that must be absorbed first. All of this means that it will be years before the impact of the Growth Plan can be assessed.