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PaperclipPerfector  16hr ago (text post)   482 thread views

Friday Fun Thread for April 3, 2026

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Civil-engineering problem of questionable importance: What is the best definition of "intersection"?

The illustrious lawyers among us will recite the legal definition (1 2): the area within the extended gutterlines of the intersecting roadways. Or, more exhaustively (the green lines in this example PDF, a rendition of this cursed location):

  • For each point where a road's gutterline stops running parallel with the road's baseline: From the point, draw a line parallel with the road's baseline. The largest shape enclosed both within such lines and within the gutterlines is the intersection.

But this definition obviously is terrible. It's wildly underinclusive, as it fails to include the large area of pavement between those extended gutterlines and the rounded corners of the intersection. And it can produce nonsensical results on oddly-shaped corners (as illustrated on the southeast leg of the example).

Civil engineers and avid pedestrians may prefer this definition (the blue lines in the example):

  • For each point where a road's gutterline stops running parallel with the road's baseline: From the point, draw a line perpendicular to the road's baseline. The largest shape enclosed both within such lines and within the gutterlines is the intersection.

However, this definition can be rather overinclusive on corners with large radii (as illustrated on the north leg of the example).

One of the more questionable achievements of my civil-engineering career was coming up with a third definition (the pink lines in the example):

  • Within the intersection, draw as many inscribed circles as possible, each osculating (tangent to, touching, kissing) three corners of the intersection. (Generally, the number of circles will be equal to the number of legs on the intersection minus two.) The largest shape enclosed both within lines joining intervisible tangency points and within the gutterlines can be considered the lower bound of the definition of the intersection.

  • For each tangency point: For each road baseline visible to that tangency point: From the tangency point, draw a line perpendicular to the baseline. The largest shape enclosed both within these lines and within the gutterlines can be considered the upper bound of the definition of the intersection. Typically, use the upper bound to determine paving limits.

  • If you need to pave farther up the side road (e. g., in order to paint a crosswalk or construct a curb ramp), just move your paving limit up the side road accordingly (still perpendicular to the side road's baseline).

Finding the center point of each inscribed circle requires an iterative solution with the parallel-offset tool, since CAD software does not have a function to find it automatically. But, IMO, this definition does a great job of drawing something that at least looks good intuitively. It still can be considered underinclusive, but it serves as the least inclusive solution that doesn't leave huge lacunae (unlike the first definition). If you want to be a little more inclusive, you can do so easily (without having to go to the extreme of the second definition). And, unlike both of the first two definitions, it works well, not just with the clean lines and arcs of proposed gutterlines, but also with the ragged line strings of a survey of existing gutterlines.

Pragmatic addendum to the third definition:

  • In rare situations, a leg of an intersection may have two corners with wildly mismatched radii, causing the triangular area of difference between the upper bound and the lower bound on that leg to be very large. In such a situation, use your engineering judgment to determine whether the lower bound, or even the first definition, rather than the upper bound, should be used as the paving limit on that leg.

The small, boring box (1 2*) that will serve as my glorious custom house is approximately halfway through its two-month construction schedule.

  • Photograph 1: Foundation walls; sewer pipes

  • Photograph 2: Slab; wall framing in progress; air compressor for nail guns

  • Photograph 3: Walls without siding; siding ready for installation

  • Photograph 4: Fancy roof trusses, eliminating the need for interior bearing walls; water pipes and electrical wires in ceiling

  • Photograph 5: Wall framing; electrical boxes

I think I overheard one of the workers joke that his shed is bigger than this house. 😈

*For room dimensions, I measure to the face of the drywall, while the contractor measures to the face of the stud. Any other discrepancies between these two drawings should not be considered material.

Months ago, I posted about how (1) South Seaside Park, a discontiguous and neglected neighborhood of Berkeley Township, had won in court the right to secede from Berkeley Township and be annexed by the contiguous municipality of Seaside Park Borough, but (2) the Seaside Park Borough council still needed to vote to accept the land transfer. Now, the Seaside Park Borough council has finally voted in agreement.

  • Mostly-paywalled news article
  • Annexation-impact study conducted by a contracted consultant (finding that annexation would decrease the property-tax rate in Seaside Park Borough by 8 percent, from 1.774 mills to 1.631 mills annually)
  • Video of council meeting
    • 5:22: Start of relevant discussion
    • 15:25: A councilor mentions that, despite widespread criticism of the impact study, she did an informal sensitivity analysis on the figure of 8 percent using a spreadsheet provided by the consultant, and "we can be off by quite a bit before it turns into a negative scenario".
    • 16:45: The mayor discusses the fact that, regarding topics that the state's sloppily-drafted neighborhood-secession statute fails to cover (e. g., debt transfer), advisory judicial opinions on those topics are not available, so Seaside Park Borough will just have to negotiate in good faith over those topics with Berkeley Township, and hope that no lawsuits emerge from those negotiations.
    • 25:39: A representative of Berkeley Township points out more sloppy drafting. South Seaside Park is defined in the secession petition as including only the inhabited part, so that's the only part that Seaside Park Borough is annexing. But Seaside Park Borough, as part of annexation, has copied-and-pasted a Berkeley Township ordinance that imposes a particular zone, not just on the inhabited part, but also on an adjacent state park that will not be annexed. (See the map that I drew previously. In drawing that map, I erroneously assumed that South Seaside Park included the state park, but it actually does not include the state park.) Seaside Park Borough's lawyer says the error will be corrected.
    • 36:11: The petition organizer makes a speech.
    • 40:58: A person points out that annexation will overturn the budget that Seaside Park Borough just adopted. The mayor explains that, after annexation, Seaside Park Borough will have to get permission from the state government to adopt an amended budget.
    • 1:43:18: The big vote

Wouldn't an intersection be, any space where cars travelling on multiple roads could legally cover?

That fails to include shoulders and neutral areas.

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