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Thread: Cul-de-sac design standards

  1. #1

    Cul-de-sac design standards

    Our highway department would prefer to see that the center circle of cul-de-sacs be paved over, as that simplifies snow plowing (and since this is northern Massachusetts, we do get a fair bit of snow). On the other hand, such circles are downright ugly for the remaining 8-9 months of the year, not to mention increasing the impervious cover. I'm also not fond of grass, as it requires mowing and fertilizer to stay nice.

    Does anyone have any alternatives? Perhaps some design standards for a reserved area on the outside of the cul-de-sac for snow, along with planting options
    for the center?

    I'm not that familiar with the real needs of the snow plow drivers. I know that we do use a combination of larger dump trucks (10 wheelers) and smaller full-size pickups for plowing (the latter are frequently indepedent contractors).

    Thanks,

    Gary

  2. #2

    Cul-de-sac design standards

    The local Zoning Administrator quizzed me on the rationale behind the 600 feet maximum length for a cul-de-sac as written in their Subdivision Regulations. Well, I could not answer and thus I find myself here searching for answers. I have since seen via this Website many variations to the cul-de-sac standard for rural areas, but I was wondering if am missing an important concept. The County in question has a growing rural residential development pressure. Why the 600 feet in the first place and what are some other unique ways to handle cul-de-sac design standards. Thanks in advance.

  3. #3

    Cul-de-sac Design Standards in County Subdivision Regulation

    Cul-de-sac length is governed by traffic volume and the need for circulation. One such standard is that a cul-de-sac should not have more than 150 ADT which translates to about 15 lots.

    Your subdivision may also have design standards for block design ... also intended to provide for traffic circulation. Most of these standards provide for a maximum blick length of 1500 feet to 1800 feet. I have always argued that a cul-de-sac is one-half block in and one-half out because the only way in and out is to travel back the same way you came in (the circulation argument). Ergo .. your maximum cul-de-sac length should be one-half your maximum block length. Accordingly, I hope your ordinance sets a maximum block length of 1200 feet.

  4. #4

    Cul-de-sac Design Standards

    This is a great question. I've seen it replied to in at least two ways:

    1. The length of cul-de-sacs was limited because fire hydrants were normally placed at the intersection rather than on the cul-de-sac street (I think I saw this explanation in one of Randall Arendt's books). The maximum length of a cul-de-sac supposedly related to the length of fire department hoses. Any longer than the standard and houses couldn't be served with the fire hydrant (obviously putting a hydrant on the cul-de-sac is a solution).

    2. It's a matter of efficiency. Cul-de-sacs have no other turnarounds and so the longer the street is, the more wasted time there is turning around.

    Other reasons: you don't need a long cul-de-sac because other design options become possible (connections, an alternative street and lot pattern, etc.). Also, there is some "aesthetic" issues involved as well--picture a straight cul-de-sac (they often are) 1500 feet long with houses all at the same setback. Like looking down a tunnel.

    This question teaches us that if we cannot articulate a good reason for the code requirement, we probably should not have it in our code. I'd keep this provision, though, for the latter reasons described above.

    Jerry Weitz

  5. #5
    Cyburbian Joe Iliff's avatar
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    Cul-de-sac Design Standards in County Subdivision Regulation

    In addition to the length of a fire hose, the answer also relates to how long a distance you expect an emergency responder to run were the entrance to the cul-de-sac blocked to vehicle traffic. Assume that no vehicular traffic could get past the intersection, and that someone in the last house needed a policeman or EMT. The longer the cul-de-sac, the longer their response time.

    This issue can be dealt with thought by having another street near the bulb of the cul-de-sac where emergency vehicles could stage if there is no barrier (fence, landscaping) to pedestrians crossing from that street to the cul-de-sac.

  6. #6

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    Cul-de-sac Design Standards in County Subdivision Regulation

    I have heard the fire hose explanation, but it is irrelevant in most rural areas, where there either is no central water, or a water system that does not support fire flows. The real issue in rural cul-de-sac design is volume. I agree with the assessment that the maximum number of homes served should be about 16, and certainly not more than 20. Using that standard length becomes a function of lot size/density, but I have often combined a number of lots with a maximum length to keep everyone happy. Maximum length I recommend? 1000 feet, maybe 1320. Another nuance: I usually recommend allowing longer culs-de-sac for small numbers of lots (say 4) on slopes becuz I am more concerned about the visual scarring and erosion, etc created by encouraging people to build more roads crossing slopes.

  7. #7

    pushing

    I know this may sound off the wall to you all. However, Cul-de-sacs are a pet peeve of mine...My solution? Hold on now... Cul-de-sac streets should be the exception and not the rule. They should be as long as necessary to extend to the next developable property, so that when it is developed the road will continue on until such time it connects with another street and there is no more cul-de-sac. The start of building an actual neighborhood rather than isolated developments, side by side, that do not in anyway relate to one another.

  8. #8
    Cyburbian mike gurnee's avatar
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    pushing

    It depends.

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