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CE 578 Highway Traffic Operations

CE 578 Highway Traffic Operations. Lecture 2 and 3: Vertical Alignment and Sight Distance. Objectives. Vertical curve design parameters Sight distance calculation Sight distance measurement Sight distance based design speed calculation. Vertical Curve Design Parameters.

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CE 578 Highway Traffic Operations

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  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 <= L • S >= 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. S Centerline intersect point Straight edge Location of subject station Sight obstruction (3.5 ft for passing) (2.75 ft for stopping) Horizontal Curve Sight Distance Measurement

  9. S Driver eye height (h1) Tangent 2 Tangent 1 Limit of passing sight distance On-coming vehicle driver eye height (h2) 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 236+00 curve • At VPC 251+00 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 242+86.8 curve • PC 283+01.7 curve • Calculate and measure the sight distance for: • VPC 236+00 curve

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