CE 578 Highway Traffic Operations

1
CE 578 Highway Traffic Operations

• Lecture 2 and 3 Vertical Alignment and Sight
  Distance

2
Objectives

• Vertical curve design parameters
• Sight distance calculation
• Sight distance measurement
• Sight distance based design speed calculation

3
Vertical Curve Design Parameters

• G1 and G2 grade at tangents 1 and 2 ()
• A change in grade ()
• E external distance (ft)
• y vertical offset from tangent 1 to point P (ft)
• L vertical curve length (ft)
• x horizontal distance from VPC to point P (ft)
• P arbitrary pointy on curve

4
Vertical Curve Design Parameters (cont.)
5
Vertical Curve Equations
6
Sight Distance Calculation

• Crest vertical curve
• S lt L
• S gt L
• Solve for S
• For passing conditions, usually sag curves not an
  issue
• Day-time conditions provide full sight of curve
• Night time conditions can see head lights of
  on-coming vehicles

7
Sight Distance Calculation (cont.)

• Horizontal curve (solve for S, use degrees)
• R radius from center of curvature to the
  middle of inside lane
• M middle ordinate or distance from sight
  obstruction to middle of inside lane

8
Horizontal Curve Sight Distance Measurement
9
Vertical Curve Sight Distance Measurement
10
Sight Distance Operational Effects

• Passing limitations
• Driver ability to pass
• Passing zone design
• Passing zone length
• Frequency
• Passing lane design
• Driver anticipation of beginning
• Speed limitations

11
Assignment Problem 1

• USE PAGE 2 OF ASSIGNMENT 1
• Calculate vertical curve design parameters
• Given
• L
• elevation of VPC
• station of VPC
• G1
• G2
• Find elevation and station of VPT and VPI
• At VPC 23600 curve
• At VPC 25100 curve

12
Assignment Problem 2

• USE PAGE 2 OF ASSIGNMENT 1
• Calculate and measure the sight distance assuming
  middle ordinate of 25 ft for
• PC 24286.8 curve
• PC 28301.7 curve
• Calculate and measure the sight distance for
• VPC 23600 curve