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Thread: Vision triangles

  1. #1
    Cyburbian mique28's avatar
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    Aug 2005
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    Vision triangles

    My research suggests that there exists a wide variety of definitions for vision/visibility triangles throughout municipal and state governments (and even ITE and AASHTO). The differences include the distance of the triangle, whether or not the intersection is controlled and the point of origin for the triangle. It is the latter, the point of origin question, which is currently the most vexing to me. The two most common options appear to be:

    1) Beginning the triangle at the intersection of right of way lines (as shown here: http://www.sturtevant-wi.gov/index.p...ge:Vision1.jpg) or;
    2) Beginning the triangle at the intersection of street edges (as shown here: http://www.qcode.us/codes/roseville/..._160&frames=on)

    I think you can clearly see how this little difference could have varying impacts on private property. I'm not really worried about what your local codes require but I am more interested in what you would find as preferable while still maintaining public safety. Thanks for the opinions!

  2. #2
    Cyburbian mike gurnee's avatar
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    You forgot the center of the roadway. Curbs and street edges can move over time with widening projects. It the road pavement is not perfectly centered you can have a few feet difference for lots across the street from each other. Right of way lines are unknown to the owner unless there has been a recent survey. For the center of the roadway, who wants to stand in the middle of a street with a tape?

    In other words, there are potential problems with each approach. I have used all three, based on the practice before being hired.

  3. #3
    Cyburbian mique28's avatar
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    Right you are. In comparing standards I did see the center line being used and even saw where some guidelines called for the center of travel lanes as the point of origin (WISDOT for example). However, the two most common appeared to be the two I described previously. Your point about roadway widening is well taken... with such a standard style zoning provision (using the pavement edge for point of origin) I guess this would be a case were you would see legal non conformances or variances. I wonder how many times you would actually run into a condition where the widened road encroached on improvements previously located outside of the triangle given the propensity of roadbuilders to secure a ton of ROW at the outset? On the flip side, using the edge of pavement for the origin of the triangle would be more responsive if the road was narrowed.

    My current leaning is that the edge of the road pavement is the best point of origin for the triangle because it generally creates safe visibility without encroaching excessively into the use of private property.
    Last edited by mique28; 18 Dec 2009 at 12:43 PM.

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