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Access

Tom R

Cyburbian
Messages
2,274
Points
25
We have been working with our county prosecutor, highway engineer, emergency management agency and the local Home Builders Association to help develop a means to determine subdivision site characteristics that should be taken into account in deciding whether more than one entrance should be required for a subdivision of what size and how many dwelling units should be on a cul-de-sac and maximum cul-de-sac length. I personally argued for connectivity to be taken into consideration along with the usual public safety factors.

Below is a list of factors for these purposes. It's very much a draft, but it's a start. Some of the factors such as traffic lend themselves to hard numbers. Many of the others do not. I envision starting with a maximum number of dwelling units if all the factors are optimal and working downward when problems are evident. I would appreciate any input regarding measures, additional factors or deletion of factors. Thanks.

Subdivision access worksheet

Factor Measure

Traffic ADT

Flood Hazard Frequency Depth
Number of crossings

Slopes Percentage
Number slope areas
Road design

Water supply Hydrant locations
Pressure

Fire ponds Location
Number

Connectivity Number of through street connections
Existing stub streets

Environmental Impact Nature of impact
Degree of impact

Sensitive land use access Schools
EMS
Hospitals

Existing land use barriers Residences
Railroads
Water bodies
Degree of development
Other

Institutional barriers Government land
Dedicated parks
 

Cardinal

Cyburbian
Messages
10,080
Points
34
It is somewhat a related issue, that we have recently begun requiring a network of public roads, connecting to the surrounding neighborhood, in larger rental multi-family developments. Connectivity is a major factor, but we also find a benefit in policing and code enforcement. In the past, we have seen MF projects developed 2000 feet deep on private drives, with one driveway. All sorts of undesirable things may happen that far off the road. Having units fronting on a public road makes it more difficlut for the owner to "defer maintenance" and for illegal activity to occur in a hidden parking lot. Most developers have grumbled, but accepted the requirement. We are fortunate in having local builders who understand the intent and genuinely want to build a good project. A few low-end types put up a struggle, but then their whole proposal often gives the appearance of only wanting to turn a fast buck by building cheaply. They tend to run afoul of the Plan Board on more than just access.
 

Tom R

Cyburbian
Messages
2,274
Points
25
lots

With the township form of government and zoning in Ohio, the county planning commission and departments have a job similar to herding earthworms. We have communities that require two entrances to a development which according to the ORC they are not empowered to do and others who love 4000' cul-de-sacs which are not permitted in our sub regs.
 
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BKM

Cyburbian
Messages
6,463
Points
29
In our draft Urban Design Guidelines, (a document that is NOT one of my finer moments :( ), we try to address this issue. There are cul-de-sacs in town where police access is severely limited because of the subdivision layout.

At a minimum, since cul-de-sacs are the goal for many builders and residents, our goal is to try for through-pedestrian and/or bicyle connections.
 

Budgie

Cyburbian
Messages
5,270
Points
30
Connectivity Ratios

Minimum connectivity ratios help quantify connectivity. Connectivity ratios have two components: links and nodes. Links include road segments between nodes (internal and external nodes). Nodes are either intersections or cul-de-sacs. Nodes external to the subdivisions are not considered in the calculation, because roads that do not link to external roads are counted as cul-de-sacs. Divide the number of links by the number of nodes to derive a ratio. A 3 x 3 block development pattern (tic-tac-toe) with all roads having extenal access would have 12 links and 4 nodes for a ratio of 3. The same grid with 4 cul-de-sacs would have 12 links and 8 nodes for a ratio of 1.5. Obviously, low ratios denote poor connectivity.
 
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