Example of a superblock in our current urban settings. Satellite image via google.
What is Advanced Dedication?
Advanced dedication is to dedicate a portion of the land area to the public right of way to achieve more substantial connectivity, accessibility, and walkability within the development. It seems a simple concept, but the existence of this incentive guideline can be traced back to the history of a city block in the United States.
City Block
City blocks form the basis of a location's urban fabric; they could be subdivided into smaller lots designated for different ownerships. The shape of the block creates the physical edge of buildings and our public spaces. Most cities encompass harmonious-sized blocks, but some have more significant variance.
Across cities in the United States, Portland in Oregon has the more fine urban grain; each block is about 200-220 square feet. On the other hand, Salt Lake City in Utah has more extensive urban grain; most blocks are about 500-600 feet long with various rectangular shapes.
The comparison of various sized block in different cities. In Washington DC, a typical sized block is about 300 by 350 feet; in New York, most of blocks shaped in rectangular with 200 by 400 feet in size; in Portland, most of them are square shape and are about 200 by 200 feet; in Salt Lake City, the blocks are larger than average block size in most American’s metropolitan cities. The size of Salt Lake City’s block are typically 600 feet in length.
Superblock
A superblock is an area bounded by arterial roads with the size of a combination of multiple standard-sized city blocks. With the influence of modernism in architecture and urban planning, these huge-sized city blocks without any cut-through passageways were popular during the 1920-1950s. That type of neighborhood also reinforced more automobile dependency.
One representative superblock project is the Radburn community in New Jersey: the network roads within the planning area are mostly dead-end streets and cul-de-sacs. The planning concept aimed to separate vehicular and pedestrian traffic. Thus, its superblocks were complemented by an internal pedestrian path that connected the entire sector.
Satellite image shows original Radburn Planning Concept scope. Image via google
Enlarged (highlight portion from image above) of Radburn Planning site in New Jersey.
Original Radburn master plan. Image via www.townandcountryplanninginfo.com
Example of Earning [Advanced Dedication] Points
Many planning divisions encourage developments to create more connectivity within the neighborhood. Take Montgomery Couty's incentive density guideline as an example; the incentive points are calculated on a sliding scale that allows up to 8 points in the LSC zone, 15 points in the EOF zone, and 30 points in the CRT and CR zone.
The formula is as follows:
D (dedicated land area) divided by N (net lot after dedication) multiple 100 will get the incentive point.
This potential site (at CR zone) has about 303,700 square feet of land, with an existing street area (including a parking lot) of 77,600 square feet. However, none of the internal streets cut through this block.
The proposed scheme has a dedicated (public) street area of 70,100 square feet, which is approximately 23-24% of the existing land (gross) area. The proposed street cuts through the block, connects to adjacent major arterial and creates a more efficient urban fabric.
This site is in CRT/CR zone and has a land area of about 303,700 square feet. 70,100 square feet of the land area is dedicated to the public right-of-way. Considering the formula, the equation is 70,100 square feet (dedicated land area)/233,600 (net lot after dedication) =30%. Thus gain 30 points.
Additional Sustainable Credit
According to one of LEED-ND Prerequisite-Connected and Open Community, locating a project with at least 90 intersections per square mile is considered a "smart location" strategy.
Images below are the example we can find in our urban area.
(As a side note, to be "counted" as eligible intersections for the connectivity credit, the path must cut through the entire block and cannot connect to a dead-end or gated circulation.)
What’s the takeaway?
A finer-grained neighborhood not only promotes multi-modal transportation, but also improves walkability and other physical activities. Which benefits overall public health. Generally, it takes an average of 20-30 mins for a pedestrian to walk a one-mile-long path. If most essential services are within walking distance, the residents will likely finish their shopping or daily chores on foot, increasing their chance of exercising.