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INTERCHANGE DESIGN Part 2

INTERCHANGE DESIGN Part 2. Fall 2013. Note: all information taken from Freeway & Interchange: Geometric Design Handbook (2005) by J.P. Leisch et al. (ITE Publication). Exit and Entrance Ramps. >50 mph 300 ft <50 mph: 250-275 ft. 400 ft to 600 ft. 400 ft to 600 ft.

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INTERCHANGE DESIGN Part 2

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  1. INTERCHANGE DESIGNPart 2 Fall 2013 Note: all information taken from Freeway & Interchange: Geometric Design Handbook (2005) by J.P. Leisch et al. (ITE Publication)

  2. Exit and Entrance Ramps >50 mph 300 ft <50 mph: 250-275 ft 400 ft to 600 ft 400 ft to 600 ft

  3. Designs for Exit Ramps Higher volumes Best capacity

  4. Designs for Exit Ramps • Taper angle too large • Reduces capacity because drivers need to decelerate significantly at the gore area

  5. Vd = ≥60 mph 16 ft 12 ft 12 ft 12 ft

  6. Designs for Entrance Ramps 400 to 1,400 vph 800 to 2,400 vph 1,500 to 3,000 vph 2,000 to 3,600 vph

  7. Vd = ≥60 mph 16 ft

  8. Exits and Entrances on Curved Highways Prevents through vehicles to enter the ramp Maintain same superelevation

  9. Exits and Entrances on Curved Highways Better to design exists on the tangent rather than on a curve

  10. Interchange Design Overview Should use Decision Sight Distance

  11. Interchange Design Overview

  12. The offset between 50 to 80 ft.

  13. Loop exit from freeway, the radius can vary between 150 and 250 ft Tangent Spiral

  14. Spiral Transitions

  15. Maximum Grades

  16. Ramp Terminal Four types for Diamond interchanges Design overlaps (left-turn lanes)

  17. Ramp Terminal Several partial cloverleaf designs

  18. Ramp Terminal • Design Principles • Design and traffic control scheme should optimize the operation quality of traffic flow • Designed to minimize crashes and their adverse effects • General guidelines • Discourage undesirable wrong-way movements • Desirable vehicle path should be clearly defined • Encourage safe vehicle speed • Traffic streams should cross at near-right angles and merge at flat angles • Provide accelerating and decelerating lanes (as well as turning bays)

  19. Ramp Terminal • Design Criteria • Design speed should be between 25 and 40 mph (gore area should be between 50 and 60 mph) • Ramp approach should meet at 90o • Left-turning radii between 50 to 75 ft • Left-Turning Radii between 120 to 200 ft (single-point) • Grades should be less than 3%

  20. Ramp Terminal Rural Design

  21. Ramp Terminal Tight-Urban Diamond

  22. Ramp Terminal

  23. Ramp Terminal

  24. Ramp Terminal

  25. Ramp Terminal

  26. Ramp Terminal

  27. Ramp Terminal

  28. Typical Cross Section One-Way Frontage Road System

  29. Typical Cross Section One-Way Frontage Road System

  30. One-Way Frontage Road System

  31. Frontage Road Design: Ramp to Cross Road Intersection

  32. Frontage Road Design: Ramp to Cross Road Intersection • Lw = length required to accomplish the weaving (lane change) in feet. • Ls= the length required for vehicle to decelerate in feet. • Lq = the length of the queue from the downstream signalized intersection in feet.

  33. Computing Lw Assumptions: Vd for ramp = 40-45 mph, but because of the driver can see the queue, the speed could be reduced by 20 mph.

  34. Computing Ls Use Stopping Sight Distance (SSD)

  35. Computing Lq LT = 350 veh/hr – 1 lane RT = 450 veh/hr – 1 lane, but 50 veh/hr RTOR TH = 800 veh/hr – 2 lanes, 400 veh/hr per lane Controlling movements: Through and Right Turn (8% trucks) Lq = 470 ft (desirable) Minimum = 360 ft

  36. Computing Lf Lf = L w + Ls + Lq Lf = 330 ft + 115 ft + 470 ft = 915 ft

  37. Summary Analysis based on hundreds of frontage road /ramp/intersection conditions

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