SIGHT DISTANCE TRIANGLES

Providing adequate sight distance at allintersections is important to protecting thetraveling public. An inability to see, andrespond to, oncoming traffic is a cause ofcrashes in Cochise County. Identifying aDriver’s Clear Zone helps property ownersprovide adequate sight distance for driversusing their designed roadway or driveway.

What are Sight Distance Triangles?Sight triangles identify areas at the corners ofintersections of roads and driveways whereviews of approaching traffic should not beobstructed. Sight distance triangles must beidentified and shown at all road intersectionsand noted on the final subdivision plat and oncommercial site plans. These areas should benoted as “minimum driver’s clear zone”, andare required to remain free of all obstructionsthat would interfere with a driver’s visibility. Thisclear zone area is defined as anythingbetween the heights of 3 ft and 10 ft, whichoften include buildings, signs, mailboxes,parked vehicles, walls/fences, vegetation etc.Exceptions (such as utility poles) may only beapproved by the County Engineer.

Sight distance triangles are based on the timeneeded for a driver to see traffic on anuncontrolled street, to then decide to turn,make the turning movement, and beginaccelerating. Sight distance triangles forapproaching traffic on both sides of anyaccessed roadway must be determined andprovided on your design plans.

See Cochise County Standard Detail CC300for additional information and requirements.

Special Notes:· A sight distance triangle is measured

from edge of pavement to edge ofpavement or, if an unpaved roadway,from the edge of the travelway.

· Determination of sight distancetriangles may also be calculated by atraffic or civil engineer, consistent withAASHTO Green Book, to provide anunobstructed view of the roadwayvisible to the driver.

· If frequent or high levels of large trucktraffic are anticipated at theapproach, increased intersection sightdistance may be warranted andshould be calculated consistent withAASHTO Green Book.

What is the Clear Zone?Minimum Driver’s Clear Zone: No screening,landscaping, vegetation, structures, parkingareas or other obstruction to visibility betweenthe heights of three and ten feet above thetop of curb or centerline grade of the streetwill be permitted within the clear zone asdefined by the sight distance triangular area.Development must be set back or restricted inorder to provide clear sight distance.

Sight Distance/Clear Zone Exhibit: The Exhibitand table below represent the typical lengthexpectation for Distance “X” along a straighttwo lane roadway to establish an adequateclear zone area.

\Sight distance calculations should be performedwhen horizontal or vertical curvature (hills orcurves in the roadway) might impact theplacement of a sight distance triangle.

Edge ofPavement

Edge ofTravel Way

Minimum Driver’sClear Zone

Minimum Driver’sClear Zone

Edge of Travel WayEdge of Pavement

What are the typical Sight Distanceconsiderations?

Horizontal Alignment/Skew: Sight distance is ameasure of visibility, and so it is preferred thatdriveways and roadways are ideally at a 90-degree angle (perpendicular) to the roadthey are accessing, for optimal and balancedview in both directions. When parcelcircumstances cannot accommodate this, areduction to a minimum of 60 degrees, maybe considered for approval by the CountyEngineer.

Vertical Alignment: When you are installing anew driveway or roadway, or re-evaluating anexisting condition, the vertical alignment ofthe roadway you are making a connectioninto should be taken into consideration. If thedriveway or roadway is placed on either sideof a crest curve, sight distance may beimpeded by the roadway crest curve.

Landscaping: Landscaping within the Right-of-Way may be permitted, in compliance withthe Roadside Design Guide, provided thatyour landscaping does not impederecommended sight distance or causevisibility problems, introduce safety hazards,and does not create the potential to damagethe road and drainage system infrastructure.

Permitting: A Right-of-Way permit is requiredprior to construction of a driveway or roadwayand/or the subsequent clearing of theminimum driver’s clear zone within theCounty’s Right-of-Way. It is your responsibilityto keep your driveway in good condition, yourculverts cleared and the driver’s clear zonefree of any obstructions.

What if my parcel access has difficultfeatures that may require specialconsiderations?Variances to the sight distance trianglestandards as contained in the Cochise CountyRoad Design & Construction Standards &Specifications for Public Improvements arerarely approved. A few exceptions may beutility poles, mailboxes, fire hydrants, etc. andmust be approved on an individual basis bythe County Engineer.

Requests for review and approval mustinclude site plans that illustrate sight distancetriangles with mitigation plans for anyobstacles still within the driver’s clear zone.

Highway and Floodplain DepartmentDesign Standards, Detail, Specifications,zoning & floodplain maps, as well as permitapplications are available in Bisbee and SierraVista. Call for Service Center locations andoffice hours or visit our website atwww.cochise.az.gov.

Sight Distance Triangle

Cochise CountyCommunity DevelopmentHighway and Floodplain Department

1415 Melody Lane, Building FBisbee, AZ 85603

520-432-9300/Fax 520-432-9337Email: highway@cochise.az.gov

www.cochise.az.gov