Intersection Sight DistanceCase C1

Ryan MillerCE 480

10/19/10

Objective

• Introduction• Approach sight triangles• Departure sight triangles• Special situations

Introduction

• Intersections with yield control on minor road• Considers crossing maneuver from minor road• Must consider both approach and departure

sight triangles• Sight distances needed by drivers exceed

those for stop-controlled approaches

Introduction

• Minor road vehicle can cross major road without stopping if no potentially conflicting vehicles on major road

• Minor road vehicle assumed to decelerate at rate of 1.5 m/s2 while traveling from decision point to intersection

• Minor road vehicle assumed to cross and clear intersection at 60% of design speed

Approach Sight Triangles

• Distance along minor street to major street (a)• Distance along major street to vehicle with

right-of-way (b)• Must check both left and right directions• Use Exhibit 9-60 to find (a)• Use equations 9-2 to find (b)

Approach Sight Triangles

Approach Sight Triangles

Approach Sight Triangles

Approach Sight Triangles

Vmajor= 45 mph Both approach grades= 0%

Vminor= 25 mph Lw= 12 ft

La=19 ft (PC)

Approach Sight Triangles

Approach Sight Triangles

a= 130 ft a=142 ft ta= 4.0 s tg= 6.5 s

b=b= 1.47Vmajortg= 1.47x45x6.5= 430 ft

Approach Sight Triangles

Departure Sight Triangles

• Departure sight triangles automatically considered

• tg must meet minimum value from exhibit 9-57 (used for B3 intersection)

Special Cases

• Major road is divided highway with narrow median–Consider additional crossing width

• Major road is divided highway with wide median–Crossing maneuver need only consider

crossing near lanes–Crossing far lanes must be accomplished

from stopped position (departure triangle)