Sight Triangle & Corner Clear. Pol. at Inters. & Driveways
Sight Triangle & Corner Clear. Pol. at Inters. & Driveways

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This informational report explores the history of corner visibility guidelines, compiles and compares the intersection corner visibility policies and practices in place in the United States and in certain foreign countries, and addresses whether policy consistency on the topic exists.

The Technical Council Committee conducted an in-depth listserv/MuniCode search using "Sight Triangles", "Corner Clearance", "Intersection Sight Distance", and other associated terms. In addition, committee members obtained municipal, local, and state government codes, policies, guidelines and handbooks related to intersection or driveway sight distance triangle regulations. A random sample of 85 guidelines from this extensive body of research (more than 850 were collected) was summarized in a database in order to identify recurring methods and requirements.

The following observations were made:
  • The AASHTO guidelines were not routinely implemented in the municipal and local government codes. States tend to base their guidelines on AASHTO more than other types of governmental entities (i.e., counties, cities, towns).
  • Many municipalities use sight visibility triangles described by equal distances along edges of pavement, property lines, or right-of-way lines instead of applying AASHTO guidelines.
  • When sightlines are laid out, the calculation methods for the distances along the major street centerline vary greatly. The most common methods include AASHTO methods in the 1990/1994 Green Books, "time gap" based methods from the 2000 and 2011 Green Books, and other arbitrary methods.
  • Most codes do not address the individual cases specified by AASHTO. Those codes that do mostly address Cases B1 (Left Turn from Stop) and B2 (Right Turn from Stop). Cases B3 (Crossing Maneuver) and F (Left Turn from Major Road) are rarely addressed.
  • There are no consistent definitions for the maximum height of a ground obstruction or for the minimum height of a tree canopy obstruction within a sight triangle.
  • The objects allowed within the sight triangle also vary. Those that seem to be regularly allowed are traffic signals, signs, and utility poles.
"POLICIES AND PRACTICES" SURVEY OF MUNICIPALITIES
The Committee prepared a survey that was distributed to all the members of the ITE Traffic Engineering and Public Agency Councils that was based on the literature and code reviews. More than 150 responses were received.
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