Professional Surveyor Magazine - September 2010
Read Part 1 Part 3 Part 4
By Richard Harrison
Prefurbia is a new way to design land developments. In part one (June 2010), we began with an existing site plan to use as the benchmark for a new plan. This installment explains the process to produce a plan that follows Prefurbia’s principles.
Design the Main Walks
Prefurbia introduces the concept of designing walks first when planning land development. You read that right: Create the main walking trails (Figure 1
) to connect through the neighborhood as the very first step.
In this example the yellow line is the main walking trail that we determined would make it easy to take a stroll directly through the neighborhood. Because the commercial area will be situated in the north region, the single-family area to the east, and the town homes along the west, we designed a system that would directly connect these areas. The main trail will be 8’ wide. Because the site is relatively flat, the walk will be tree-lined, creating a canopy as the neighborhood ages.
Set the Street Patterns
A basic guideline of Prefurbia is that streets should not parallel a boundary line. A problem with the conventional form of design—working the streets internally from the boundary on a geometric grid—is that it guarantees the site will be filled with streets, not homes.
Prefurbia embraces fluid design, but not traffic circles. The original plan in this example had all the main streets intersecting at a traffic circle. Prefurbia design maintains a constant rate of traffic flow, so traffic circles are not included unless they are absolutely mandated by the municipality.
Consider also that the original design had the main entrance to the west. We do not want to carry heavy traffic through the single-family area (those homes have driveways along the street), and traffic should instead flow to the retail shops (to help businesses succeed).
Another guideline is to minimize collector street length, for two very important reasons. One, of course, is cost, but more important is that collector streets tend to have some areas of non-frontage (this is waste), and any excessive street you build translates into less area for housing and less lease-able square footage for commercial development.
There are an infinite number of design alternatives on any site. Prefurbia’s free-flow nature provides more viable options than simply designing streets by working the geometry inwards. This example shows just one option, and keep in mind perfection is not possible—every design is bound to have flaws. What we do want is a balanced design, not heavily weighted to just economics or just environment.
We decided to create a main collector (Figure 2
) that swings to the east, then heads northwest (across an existing street intersecting the north boundary road), and then to the drainage ditch at the northwest corner of the site. The thick blue line represents the main collector that curves to the site then reverses back to exit the site. It crosses the main trail twice (you will see later how we safely handle this situation). At the neighborhood entrance there is a constant rate of flow maintained without the need to stop along this street.
Another reason to swing the major street to the northwest is to create a “superblock” for the commercial area and not break it into two separate areas. Also, in the neighborhood entrance the open space for the drainage area along the west line will provide a welcoming space.
Finally, set the single-family public street (Figure 3
). This street should discourage speeding and maintain a constant rate of flow. This is the only area that will use coving. (Prefurbia is not about coving, and a coved development does not fall into the Prefurbia category. Coving is strictly a meandering streetscape.) In this instance, coving works wonders to enhance curb appeal and economics while reducing environmental impacts. The street in the single-family region will handle a much lower traffic load and discourage people from cutting through a neighborhood to try to save time.
Design Lot Geometry
With the street patterns set, next you need to put on your land surveyor’s hat to start thinking about the intricacies of the lot geometry. Note that we intend to use the east street as frontage for single-family lots in this situation; because it is a low-traffic residential street it’s always best to use frontage that is already available, when possible.
What you see here has been prepared within Prefurbia’s Performance Planning System (PPS) software but has been edited for the clarity of this article. The reality is that the initial sketches should always be done with pencil and paper at a known scale, especially when you’re departing from a pattern in which you simply parallel the boundary. (To learn how we use the hand-sketched drawing on this site as the basis for accurate coordinate geometry, click here
After designing the major pedestrian and vehicular patterns, it’s time to concentrate on the geometry of the streets (Figure 4
). A decade ago I published articles in this magazine on how to design coved subdivisions; I said to lay out the homes first, then design the streets. However, once you have enough experience with coving you will be conditioned to know which street patterns will be most efficient. This is why we design the streets second (with the trails first).
By activating the centerline layer and using PPS’s “length of elements on active layer,” we find the length of street in this design is 4006.5 feet. On the original plan (we corrected the single-family streets from private to public) there are 5,490 linear feet. We reduced the length of the public street by 27 percent!
Because we reduced the length of the street by 1,484 feet, we picked up 1.7 acres in land (not needing to build that much in 50’ ROW). With this extra land we can insert meandering islands along the main street; these are called traffic diffusers. Although diffusers are a matter of style, making the design look cool is not why we chose them. When we design a neighborhood where pedestrians are likely to cross higher-traffic streets, diffusers particularly help.
A roundabout destroys flow, and a pedestrian crossing at one of these is a challenge because cars are looking to avoid other cars, not concentrating on that pedestrian outside their line of sight. (For more on this click here
.) A diffuser, however, maintains flow on the primary street. More importantly, it also allows the pedestrian to be directly in the line of site of vehicles and allows crossing at one-way lanes. The recent book Gridlock by Randall O’Toole refers to studies proving this type of crossing reduces pedestrian accidents by 33 percent. The diffuser signifies an entrance to a new land use and offers the advantages of a roundabout with greater efficiency.
Island variation eliminates monotony and creates enough distance for the pedestrian or bicyclist to concentrate on traffic. Also, some of these island areas are large enough for rain gardens to filter the run-off.
The total public street paving with the diffusers having 20’-wide one-way lanes (we established this as a minimum with the city on prior planning) is 163,440 sq.ft. Compared to the original plan, which computes to 182,716 sq.ft., it at first appears we have reduced the paving by only 11 percent, but keep in mind that the prior plan used 26’ and 24’ width on public streets with 12’ width on one-way lanes. By increasing the widths to 34’ and 20’ (one ways) as required by regulations, we get 30 percent or more reduction in overall street paving. How much do you think the developer and the city will appreciate the 30 percent reduction in initial- and ongoing-maintenance costs?
Consider the Floor Plans
The next step is to place the lots, right? Wrong. Your job as a land surveyor platting others’ designs might be to compute and follow the plan, but this series of articles is about Prefurbia, not traditional subdivision platting. Once you cross the line from subdivision to Prefurbia, a whole new set of methods is at your disposal. Subdivision platting concentrates on lot generation with perhaps the home pad (the maximum-sized home) as an additional control. Prefurbia blends the spaces within the home as a function of the overall neighborhood plan. It also prescribes to shape the home to the shape of the lot.
A decade ago, we taught how to use the home pad with minimum yard (front, side, and rear) as temporary guidelines to set homes and design lots for coving. Prefurbia expands on this design technique by integrating how the floor plan functions within the lot (Figure 5
). We essentially have three shapes of lots—the rectangular, an inside pie (inside the arc), and the outside pie (outside the arc). Coving creates additional space between the homes, and Prefurbia is about space management and the elimination of waste. Consider where the main living areas are. Consider also window locations to be assured that the space you create can actually be viewed from within the home.
The light blue area symbolizes a pad that conventional subdividing would dictate. Note the middle “inner arc” home, which is expanded along the street frontage. The garage is no longer as prominent, and living spaces now tie to the streetscape. The outer pie home shaped to the lot (on the right) expands the living spaces to the rear yard area. With both inner and outer pie-shaped homes, the depth of the home is less than the rectangular lot, thus allowing for more space in the rear yard.
Also note the location of the kitchens. In the United States the kitchen is where the family and guests tend to gather; thus the kitchen becomes a focal point for space. By paying attention to the interior of the home as part of the process of subdividing land, you have just significantly increased its value. (This design technique is covered extensively in the teachings included within PPS.)
The original floor plan for the town homes (Figure 6
) was overall a good layout. The garage side of these units will be the rear entry, with the living area side being the front. The front consists of a concrete patio and sliding glass doors; that is not consistent with the porch look we want on this site plan.
Prefurbia prescribes always to showcase the best-looking side of the home, and because of economics that is typically only one of the four available sides. When you plat subdivisions, the façade is typically ignored. This is why most subdivisions lack character and showcase poorly.
Look at the length of sidewalk to the entry of the home on the two inner units. This complex entry reduces space, decreases livable area, and increases construction costs. Now is the time to point out any design suggestions to the developer, who can afterwards approach the architect with any changes.
illustrates the new town home floor plan with minor changes. Patios are now porches with walks extending from them. The original end units entered from the side; now they have much less walkway, which means less expense and less impervious surface area. Floor plans were modified (they were pretty good to begin with) to minimize construction costs and maximize useable space. These changes essentially pay for the more expensive front porch and additional architectural elements that will make this a great neighborhood to live in.
So this begs the next question: Why would a land surveyor get involved with the floor plan? If you don’t, who will? The developer will surely appreciate your comments (whether they choose to use them or not) and will place your firm above others.
To be continued in part three.
Rick Harrison, author of Prefurbia and creator of Coving, is president of Rick Harrison Site Design Studio, which offers cutting-edge design solutions that enhance quality of life with the beauty of the natural environment. His technology, Performance Planning System, is marketed through Neighborhood Innovations, LLC.
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