What Density Is Right for Central Brookhaven?

More dense development is spun into Brookhaven’s DNA.  Since the planning of the north MARTA line in the 1970s and the decision by MARTA and DeKalb County to locate a MARTA station along Peachtree at Dresden, it has been understood that the area would redevelop with more density.  It is a basic urban planning principle that mass transit stations are located in dense urban nodes–mass transit economics depend on a critical mass of riders, and that means serving locations where people live and where they want to go.

Brookhaven is ‘just up Peachtree’ (Atlanta’s Main Street) from Lenox.  Several “station area” planning studies have been done over the years showing taller buildings and greater density around the MARTA station, with the LCI Study plan and the MARTA Charrette plan being the most recent.  It has taken longer for re-development to come to Brookhaven than planners predicted, but it appears that now it is imminent.

How is Density Measured?

Density can be measured in at least three different ways for planning purposes.

Units/acre is a common measure of residential density: its limitation is that it only accounts for people who make their home in the defined area.

Floor Area Ratio (FAR) is another common measure: it measures overall building density by comparing building floor area to land area.  It does not distinguish by building use, and it assumes that the people using each building will be roughly proportional to building floor area. Its advantage is that it presumably includes both people who live in an area and people who work or visit an area.

Occupants/area is a third measure, with “area”in this ratio usually being a square block or square mile. This is usually an after-the-fact empirical measurement and can be difficult to use for presciptive planning criteria.

The Brookhaven-Peachtree Overlay Zoning District uses, by implication, an FAR approach. It specifies a footprint size and building height, resulting in a building volume that can be used for any of a mix of specified uses.  It encourages ground floor retail space but doesn’t require it.  Brookhaven currently interprets the Overlay as not specifying residential densities, meaning that the Overlay’s FAR approach can only be applied if no residential units are included in a development.  This interpretation has the net effect of requiring all new development that includes housing to go through a public hearing and rezoning process to determine the housing density.

There are two separate, but related, ways to understand density for central Brookhaven:  1) what is the right density from an urban planning perspective?, and 2) what is the right density from an economic (and property rights) perspective?


The Urban Planning Approach

So what density is right for central Brookhaven?  The LCI Study (Urban Collage, 2005) suggested a density and use mix as did the MARTA Study (EDAW, 2009).  Their recommendations are summarized in the chart below.

As to an optimal density, there is no factual answer in the urban planning universe other than, “a fairly dense urban development is an essential feature of a successful public transit system.”  That’s taken from a 2011 Cal-Berkeley study entitled “Urban Densities and Transit: A Multi-Dimensional Perspective” ( UC-Berkeley Study)  The study goes on to review 24 mass transit systems in major cities throughout the US (including Atlanta), and the authors conclude that 45 residents per gross acre within a ½ mile radius of a heavy rail station is a sound number for financial viability.  They also conclude that what’s as or more important than nearby residents to a mass-transit station’s success are JOBS concentrated within a ¼ mile radius of the station. “The magnitude of the relationship between employment density and transit ridership is twice as large as that between residential density and transit ridership.” ” (PPIC Report “Making the Most of Transit”).

So what is the right mix of jobs and residents to support a MARTA station?  From two more studies, we learn that MARTA rail has cost about $175 million per mile (Transportation Decision Making: Principles of Project Evaluation and Programming, Sinha and Labi) and that at least 145 jobs and/or people are needed per acre within a ½ mile radius to support a rail station associated with that level of capital expense (UCTC Study).

[Reader warning: math alert! …next 2 paragraphs. Skip down to the chart if you don’t care how the numbers are arrived at.]

Doing the math, one can conclude that a healthy density for areas within ¼ mile of a mass transit station would provide 45 residents and 100 jobs per gross acre.** If we assume one gross acre results in 0.5 net acres of developable land, that results in 90 residents and 200 jobs per developable acre.  Extrapolating to actual building area, we can posit about 60 residential units and 60,000 SF of office/retail space (300 SF/employee) per developable acre as a healthy development density for a heavy rail station like Brookhaven.

These numbers actually work well with the building heights and footprints allowed in the Brookhaven-Peachtree Overlay District at the MARTA station (Subarea 1—along Peachtree and around MARTA).  The Overlay allows 6 story buildings in Subarea 1—with up to 2 bonus stories for providing certain public benefits.  By back-of-the-envelope calculation, we can assume residential units at 1200 SF gross x 60 units = 72,000 SF/acre.  Add to that 60,000 SF of office/retail area and we get a total of 132,000 SF of developed building per gross acre of land.  If we assume 50% net development efficiency per acre–allowing for streets, sidewalks, parking and open space—we end up with 21,780 SF of available building footprint per gross acre of land.  From this, we can project 6 story buildings (132,000 SF/21,780 SF) to accommodate, approximately, the projected building area.


MARTA Station Densities from Various Urban Planning Analyses

                        Residential     Hotel/Office Retail/         Library/             Parking

(Units)            Commercial  Restaurant      Civic             (spaces)


LCI Study            300                 200,000          40,000            18,000+             1600


MARTA Study    575               200,000          unspecified       18,000+             2000

(EDAW, 2008)

UC-Berkeley,    600               600,000           included           included         unspecified

et al.

**The resident/jobs mix can be viewed as averaged over several transit stations.  Thus if one transit station—say, Lenox—is heavy on jobs, another—say, Brookhaven—could overweight residences.


The Development Economics Approach

Let’s look at this further, this time from an development economics perspective.  The real estate market sets property values, and property values drive development density.  Central Brookhaven has two recent apartment developments on Dresden we can look to for market land value.  @1377 paid $1.6 M/acre for land (2012) according to property records, netting 65 units/acre on the property, or roughly $24,000/unit;  Brookhaven Alta paid $2.2 M/acre (2012), and netted 73 units/acre, or $29,000/unit.  Property on Peachtree, we can fairly assume, will be somewhat higher—currently asking prices are $2.5-3.0 M/acre. For a purely residential project then, we can expect densities in the 80 – 100 unit/acre range to maintain a workable land/unit price.  To the extent that office/retail space is added to the mix, fewer residential units are needed.

In fact, MARTA owns much of the developable land in central Brookhaven and has shown willingness to use pricing flexibility to get the type of development it wants.  MARTA will likely accept a somewhat lower-than-market land price, for example, that allows developers to include some affordable housing and significant green space on the Brookhaven site, as well as to build MARTA’s required replacement parking.


Property Rights and Density

To the extent there is strong building precedent in the area, the property values established by recent prior buildings help determine a minimum “legal” price for property.  Due to basic American liberties, named in or extrapolated from the US Constitution, property owners have rights that allow them a “reasonable economic use of their property.” In practice, this comes down to “a similar economic return to that of one’s neighbors” or “an economic use that’s supported by public planning.”  Property rights, in other words, underpin the land values and anticipated density of the properties in central Brookhaven.  If a would-be developer is not satisfied with the density Brookhaven agrees to permit, he/she can make the case to Superior Court based on property rights principles.

To be clear, the data presented above are projections of the most general nature, and the economics of each specific location—land cost, infrastructure cost, construction cost, market demand & pricing—drives the density and use mix of any specific project such as Brookhaven.  Urban planning analysis can help us make projections, but hard development proposals will tell us what is real.

If we accept the need for modest density, the question becomes, what kind of development?  Apartments?  Offices?  Retail centers?  We as Brookhaven citizens have had something to say about this through the LCI Study and Charrette processes and have said, “a mixture” because a mixture of uses creates an urban center that is most livable and sustainable.  We will get to reiterate our views in the public rezoning process that is sure to be part of most new development.

This leads us to another question—why mixed-use?  This will be the subject of a future post.

Speak Your Mind