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Dear L.A.R.E.y — Roadway Site Distance in Curve: Daylighting a Curve

Studying for the licensing exam? L.A.R.E.y has the answers. Brought to you by the ASLA LARE Prep Committee, including seasoned professionals, LARE Prep instructors, and recent and current test-takers, L.A.R.E.y’s answers will reflect the committee’s collective insights and experience. Please note that ASLA only endorses resources and materials provided by ASLA and CLARB.

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Dear L.A.R.E.y,
First, thank you for providing study materials and podcasts. They have been very helpful as I've maneuvered through the first two Sections of the LARE exams. I am currently preparing for Sections 3 & 4. In previewing the study materials, I came across the page for “Roadway Site Distance in Curve Daylighting a Curve.” I have no idea what to do with this without dimensions or scale, and when I google the information, a significant equation comes up that also requires pieces of data to be known. I need more on this topic because I do not know anything about it. Is there a missing page or some other reference material you could provide on this?
Thank you. 

Jennifer in Utah

Dear Jennifer,

Congratulations on your successes and thank you for taking our LARE Prep Course! While CLARB is unlikely to require mathematical calculations for sight distance lines, the Roadway Site Distance in Curve study material is a good example of some of the basic safety diagrams you may encounter on the exam. At the time this diagram was written, in late 2010, CLARB was asking candidates to grade out various roadway situations to resolve vehicular safety issues—for example, daylighting a curve. CLARB would provide a diagram similar to what is on the sheet and ask for a grading plan to resolve the safety issue.

Download Updated Roadway Site Distance in Curve (PDF)

If CLARB did require a mathematical calculation for sight distance lines, CLARB would provide a sight distance table to answer the question. If that ends up being the case, sight distances for vertical curves can be determined by measuring from the height of the eye to the height of the object.

Here are some terms and issues a person should understand when Daylighting a Curve:

  • Sight Distance
  • Apex
  • Height of Driver’s Eye (3.75 feet)
  • Height of Object (0.5 feet)
  • Safe Stopping Sight Distance
  • Horizontal Alignment
  • Vertical Alignment

Site Engineering for Landscape Architects by Strom, Nathan and Woland have a good description of these terms.

Good luck!


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