City of Frisco Engineering Standards

Engineering Standards
Version 6/19/12
Residential Street
15 Ft.
ROW
5 Ft.
Alley
C. Sight Line Triangles
FIGURE 2.29: Corner Visibility Triangle for an Alley
1. The sight line triangle is formed by first extending a line along the center line of the proposed
thoroughfare or driveway that begins at the tangent curb of the intersecting thoroughfare and
extends to its endpoint fifteen feet (15’) into the proposed thoroughfare or driveway. For the
sight line triangle to the left, construct a second imaginary line that is parallel to and five feet
(5’) out from the intersecting thoroughfare’s curb that begins at the centerline of the side
street and continues to the left for a distance L (see Table 2.13) to its endpoint. To complete
the sight line triangle, connect the endpoints of the first two lines as shown in Figures 2.30
and 2.31. In the case of the sight line triangle to the right, the second imaginary line is
parallel and five feet (5’) out from the nearest edge of the conflicting traffic flow (or adjacent
median in the event of a divided thoroughfare). It begins at the centerline of the side street
and continues to the right for a distance R (see Table 2.13) to its endpoint. See Figures 2.30
and 2.31.
2. Distance to driver’s eye for driveways that intersect a street is fifteen feet (15’) from the
intersecting curb line as shown in Figures 2.30 and 2.31.
3. In the case where the thoroughfare contains existing horizontal curvature, the distances L and
R must be measured along the horizontal curve.
Section 2 – Thoroughfare Design Requirements May 2012 Page 2-48