I am currently using a radii around one of our potential sites and am trying to calculate how many intersections are within that radius. The only problem is I am not sure what is considered an intersection. I would assume it is where two converging roads intersect, however I have (what appears from a satellite map) residential homes with long driveways that converge with a road. Would that be considered an intersection? If they were commercial driveways would that change the context and make them intersections?
As this is a bit of a tedious procedure I would like to do it correct the first time.
Thanks,
Tim
Eliot Allen
LEED AP-ND, PrincipalCriterion Planners
LEEDuser Expert
303 thumbs up
February 4, 2013 - 1:25 pm
Tim, for SLLc1 Option 2 connectivity, first be sure you're measuring a 1/2 mile distance around the full circumference of your project boundary, what's called a 'buffer' distance in GIS. Then using the definitions of 'connectivity' and 'street' for guidance, count the number of eligible street intersections in that area. Those that can't be counted are private residential or commercial driveway intersections with streets, alley-to-alley intersections, intersections leading to cul-de-sacs, or intersections leading to and located within areas having a single ingress/egress point.
Eliot
Timothy Nabholz
Miljöcertifieringsingenior (Environmental Certification Engineer)Skanska
3 thumbs up
February 5, 2013 - 2:39 am
Hey Eliot,
Thanks for the quick reply, you have cleared this up quite well with your definition of "street". You also reminded me again that the requirement is for the full mile radius. I had been using the .5 mile radius previously, as I had been thinking that the credit was requiring so many intersections within that radius, but it actually is intersections per sq mile, based off of that .5 mile radius. I would note to others working on this credit that the table on page 90 in the ND ref guide does a good job explaining the formula to use. Graph d) on page 93 does a similarly good job pointing out intersections .
As it was a little tough finding a good site to place a radius around the site I would recommend the site I have been using: http://www.freemaptools.com/radius-around-point.htm . From there I extracted the kml file and looked at the map on google earth. It still is quite difficult to tell what is an alleyway or driveway vs street, but it is a far better way to look at the radius.
Eliot Allen
LEED AP-ND, PrincipalCriterion Planners
LEEDuser Expert
303 thumbs up
February 5, 2013 - 10:50 am
Tim, the radius-drawing web tool is cool, but calculating intersection density requires a buffer distance around the project boundary, not a radius from a single point. And the SLLc1 distance is a 0.5 mile buffer, not 1 mile. In the Reference Guide Getting Started chapter, Figures 3(c) and (d) illustrate a buffer measurement around a project boundary, where'll you'll see the outer buffer limit shape parallels the shape of the project boundary because it is being measured at a constant distance moving around the boundary circumference. Once you determine the land area inside the buffer, after exclusions, you divide the number of eligible intersections in the buffer by the net buffer area to get intersections per sq mile, e.g. 50 intersections in a 0.75 sq mile net buffer has 67 intersections/sq mi (50/0.75 = 0.666). The Getting Started chapter has a section on calculating intersection density with more details.
Eliot
Eliot Allen
LEED AP-ND, PrincipalCriterion Planners
LEEDuser Expert
303 thumbs up
February 5, 2013 - 11:35 am
Tim, I should add one more SLLc1 Option 2 connectivity comment about the treatment of any existing intersections inside the project boundary. If such intersections weren't constructed or funded by the project developer, they may be counted. In such cases the phrase "within 1/2 mile of the project boundary" means 1/2 mile buffer on both sides of the boundary, both external and internal. If the project's total area is relatively small, the internal provision may encompass all land inside the boundary. This is why the Reference Guide page 90 Equation 3 includes the net project land area in the calculation's denominator, because the project's three internal intersections are being counted.
Eliot