Introduction

How do we build functional, sustainable urban communities? This is an increasingly critical question as the proportion of global population tilts more and more to city living. Urban density is an unignorable component in the equation — but not all density is created equal. Successful, eco-friendly city space can be dense; indeed, in some ways, a lack of sprawl creates increased opportunity for resource efficiency. But it requires thoughtful design, multi-purpose functionality, and mindful site selection. One of the best examples of this type of community is the transit-oriented development (TOD), particularly when it incorporates green space as a core principle.

City Density and the Congress for New Urbanism

The Congress for New Urbanism (CNU) in their 2023 conference took city density as a theme, discussing its benefits and drawbacks as well as what makes certain urban density more viable than others. In a review of the event’s salient discourse, writer Philip Langdon explains that “When done well, density has much to offer. By bringing large numbers of people together, it can make public transit possible. It can help shops, restaurants, and other enterprises thrive. It can entice people to walk rather than drive… It can reduce stress on the natural environment, by using resources more efficiently and emitting fewer greenhouse gases than sprawl does.”

This is a useful way to understand what makes successful urban density: building a functional community with shared, available resources (in contrast to, as CNU chapter president Dhiru Thadani called it, “warehousing people in large buildings”). Scott Bernstein, cofounder of the Center for Neighborhood Technology, suggests that dense versus non-dense is perhaps the wrong way to look at it, instead preferring the term compact: “Compactness is an economic and ecological boon. With compact neighborhoods, people don’t have to own so many cars. We should be aiming for complete communities.”

Reducing residents’ reliance on car travel is indeed an important component of successful urban community building. The more amenities available within walking distance, the less need residents have to use their carbon-emitting automobiles. But, to quote the traditional real estate adage, there’s another crucial consideration: location, location, location.

Where should we build these neighborhoods? It only makes sense, when encouraging residents to utilize public transit in lieu of their cars and to maximize access to these community amenities for non-residents, to put it near a transit station. Behold, the transit-oriented development (TOD).

Why TODs?

What is a transit-oriented development? A TOD is a “type of urban development that maximizes the amount of residential, business, and leisure space within walking distance of public transport.” Putting people in a neighborhood with numerous simultaneous day-to-day necessities — from restaurants and grocery stores to workspace and retail options — and then putting that neighborhood within walking distance of public transit is an efficient city planning strategy. An article by Smart Cities Dive states that “Many cities are currently growing with a ‘3D’ model of development — distant, dispersed, and disconnected. Transit-oriented development (TOD) is a ‘3C’ model for development — compact, connected, and coordinated.”

Mixed-use land utilization is another advantage of TOD, also noted by Smart Cities Dive: “Many current housing developments — particularly affordable housing — are not located near urban services and commercial activity. This gap… creates real costs for both people and governments. In addition to the direct costs of travel fares, sprawl wastes the opportunity to generate income at a local level. On the other hand, mixed land use enhances economic activity by diversifying the types of goods and services readily accessible.”

Developing mixed-use space is an essential element of successful TODs. This is beneficial not only for the residents within these developments, but to the larger local economy (which gives both the city and local business a financial interest in the success of the community). Diversifying the usage of space likewise allows for more efficient resource management. The Institute for Transportation & Development Policy explains that “It takes more energy, more resources, and more land to service car-oriented development than transit-oriented development.” Compact efficiency with reduced energy costs.

Well-designed TODs also incorporate a diversity of socioeconomics — including access to affordable housing options. The Institute for Transportation & Development goes on to say that “By ensuring a good walking environment and linking to high-capacity transit, TOD prioritizes the modes that many low-income people, marginalized groups, women, and caregivers use daily. Most importantly, with TOD, mixed-income and mixed-use development make it possible for people of all income levels to live within walking distance of basic services, jobs, and transit.”

Sustainability and Embracing Green Space

Michael James, General Manager at DeepRoot Canada and project lead for numerous TOD Silva Cell projects across the country, discusses the advantages of transit-oriented developments: “Increased density provides the economies of scale to make building transit corridors viable. The transit hub/station becomes a key place to put more people and services.”

Urban density does, however, present environmental challenges. As James notes, “Once you increase density around transit hubs, you by default increase the number of hardscapes, heat islands, stormwater runoff, and lack of natural green space.” It’s important for these developments to prioritize sustainability, often in the form of green space in general and urban forestry in particular.

One of the design methods for accomplishing this objective is to build pedestrian-friendly infrastructure (as opposed to car-dominated infrastructure). This strategy has numerous concurrent benefits. Firstly, as previously noted, carbon-emitting vehicles are one of the greatest contributors of climate change. By lowering their primacy, however, we can also minimize the number of car parking zones required in new developments — which in turn reduces the heat island effect. Urban Land in a piece exploring the synergy of TOD and green space states that “Surface parking, which consumes up to half the land in many U.S. suburban multifamily residential complexes, can be scaled back in high-quality transit settings and replaced by green space for play, socializing, and interaction among neighbors.”

So, not only can paved parking areas be reduced — they can replaced by thoughtfully designed green space. A report by OTAK and Puget Sound Regional Council outlining the benefits of utilizing greenery in TOD suggests that “The best results in creating sustainable communities can happen when green building is an integral part of transit-oriented development. Green transit-oriented developments that address all scales — district, neighborhood, infrastructure, street, site, and building — will result in the most benefits. The report also states that “sustainable transit-oriented development has the potential to create carbon footprints that are 35 percent less than those of conventional developments, and sometimes more.”

James echoes this in his discussion of city trees in particular: “Growing mature trees, and the associated soil volumes necessary to do so, is a key strategy to mitigating some of the negative environmental effects of densification. The canopy of large, mature trees will reduce the heat island effect and intercept large volumes of stormwater. Having a vigorous, large, green canopy on the street or in the public plazas also contributes to the ‘livability’ of these transit hubs with their numerous mental and physical health benefits.”

Successful TODs

The following are some terrific examples of successful transit-oriented developments, each one using Silva Cells to help grow large, shady trees as part of their green infrastructure strategy.

BRENTWOOD MALL

BURNABY, BC

Transforming from a sleepy retail mall to a thriving urban retail and residential center, Brentwood Mall in Burnaby, British Columbia, is a prime example of flourishing transit-oriented development. Over 100 trees are incorporated throughout the area (situated above an underground parking facility) — and the district’s success is leading to even more development in the neighborhood. Learn more by reading our case study.

TRINITY MILLS

CARROLLTON, TX

Located in Carrollton, Texas, the Trinity Mills development is on its way to becoming the largest TOD in the Dallas Metroplex. The first component to be complete (in 2022) was its center esplanade, which will serve as the core of a new mixed-use district with retail, residential, and commercial options and which includes dozens of hardscape trees planted in Silva Cells for ongoing health and vitality. Learn more by reading our case study.

DOWNTOWN ROWLETT

ROWLETT, TX

With the new light rail station built adjacent to its heritage downtown, city officials in Rowlett took the opportunity to redevelop the community into a transit-oriented development. Two phases of street trees were planted in Silva Cells with the trees already on their way to maturity, lowering the ambient temperature and reducing the area’s heat island effect. Learn more by reading our case study.

HINE PROJECT

WASHINGTON DC

A mixed-use development in the Capitol Hill neighborhood of Washington DC, the Hine Project was built with transit accessibility in mind, situated adjacent to the McPherson Square Metrorail Station on Pennsylvania Avenue. Seventeen trees are lining the streetscape and providing shady greenery for pedestrians and residents alike. Learn more by reading our case study.