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Opinion: Rethinking Subdivision Design

January 27, 2010
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As the economy begins a slow recovery and subdivision development work again gets under way, it makes sense to reassess the approach to the basic form of land development design. Developers assume that when they hire a land surveyor to subdivide their land, the surveyor will produce the most efficient, attractive and marketable layout. So what is the optimum layout?

As the economy begins a slow recovery and subdivision development work again gets under way, it makes sense to reassess the approach to the basic form of land development design. Land surveyors are a major source for the design of land developments-in particular, suburbia. Developers assume that when they hire a land surveyor to subdivide their land, the surveyor will produce the most efficient, attractive and marketable layout. So what is the optimum layout?

One of the most popular suburban subdivision design elements is the cul-de-sac. Developers and real estate agents love cul-de-sacs because they are highly desirable and, thus, easy to sell. Cul-de-sac lots have a huge rear yard (bringing premium prices) because of the extreme pie shape, and the curving streets guarantee that no traffic will speeding through. The wide angles between the adjacent home sides allow some useable side yard space as well as added privacy. Quiet, serene and safe-what’s not to love?

The reality is that existing design guidelines for cul-de-sacs create a substantial amount of waste with relatively little benefit. In the upper Midwest, for example, design guidelines stipulate that a cul-de-sac must have a 120-foot-diameter right-of-way with a 100-foot to 110-foot circle of asphalt because fire departments say they need that much room to turn a fire engine around. As a result, a typical cul-de-sac consumes 8,500 square feet of paved space. Yet, a bit farther south, those dimensions change to a 100-foot-diameter right-of-way with a 90-foot-diameter circle for a total of just under 6,000 square feet of space. That’s a substantial difference.

There are other problems, too. An 8,500-square-foot volume of cul-de-sac paving for four lots equates to 2,150 square feet per home, which is 40 percent more paving per house than a home along a typical straight street. This means the home will cost the city 40 percent more for snow removal, resurfacing, etc., forever. Additionally, cul-de-sacs have no connectivity or flow of space. And homes that are placed to offer premium views to their occupants typically form a visual barrier to others of that view.

A collection of new methods called prefurbia (preferred urbia) throws out convention in favor of a more-efficient design.

A conventional cul-de-sac design.

Bigger is Better

When planning subdivisions, everyone generally assumes that the minimum dimensions are the most efficient. However, the minimum dimensions in a cul-de-sac are typically very inefficient.

By making a typical northern cul-de-sac larger-for example, 160 feet in diameter with a one way narrow lane (18 feet wide) incorporating an organic island (see picture below right)-the pavement area plummets. Such a design uses 10 percent less paving and has a central “park” that beautifies the landscape and allows for drainage.

Placing the homes at a deeper setback from the right-of-way (40 or 50 feet or more instead of the typical 25-foot setback) stretches the length of setback line and makes the lots much less pie-shaped. Most ordinances allow setbacks to be extended without asking for a planned unit development (PUD) permit because ordinances specify only minimums, and these dimensions are all larger.

A prefurbia cul-de-sac design.

The new cul-de-sac should double the number of premium positioned and shaped lots with much less paving. Instead of being 40 percent less efficient than a rectangular lot on a straight street, the new cul-de-sac is approximately 20 percent more efficient. First developed as coving (a method of organized meandering setbacks) this larger cul-de-sac conforms to conventional design, as well-the development does not have to be “coved.”

What’s more, the larger cul-de-sac requires no more land area (density per unit) than a traditional cul-de-sac. While a lot in this larger cul-de-sac is less pie shaped, it still has a significantly larger rear yard. Additionally, the lots overlooking an 8,800 -square-foot park will be of much higher value than those overlooking the 8,500-square-feet of asphalt in a traditional cul-de-sac design. The park can be used for gardens and recreation. Another benefit is that draining into the center eliminates curbing on one side, which makes the subdivision even more efficient and green. Additionally, since the design doubles the number of premium cul-de-sac lots using less paving and overall land area, fewer cul-de-sacs-and therefore fewer intersections-are needed, which increases the efficiency of the overall neighborhood.

This design also ushers in a new era of pedestrian connectivity. Instead of a narrow sidewalk on both sides of the street, this new form of cul-de-sac features a more environmentally friendly, less expensive 6-foot walkway on one side of the street that extends through and beyond the cul-de-sac and leads to the park areas in the middle. The interconnecting walks can be made wide enough at certain locations to provide emergency access that would rival tight grid patterns.

The deeper setbacks produce longer driveways, but new design and construction methods can get the pavement volume close to that of a standard driveway and heighten curb appeal.



Embracing a New Design

Since all minimums and setbacks extend beyond the minimum required dimension, there should be no arguments from the municipality. In fact, municipal officials are likely to embrace this type of design. Also, this design allows developers to become inventive. Neighborhoods developed through this design enhance the sense of space, reduce impervious surface area, create more-affordable homes and lessen the environmental impact of land development. Even if you do not subscribe to coving, few can argue the advantages of creating this new form of cul-de-sac. Understanding this advanced method of subdivision design can help surveyors leverage more business as the economy regains momentum.


What do you think? Does this new form of cul-de-sac design offer new opportunities for surveyors in land development work? Please share your comments below.

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