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SPACING STANDARDS

SPACING STANDARDS

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SPACING STANDARDS

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  1. SPACING STANDARDS Access Implementation SAC Meeting 10-7-04

  2. Work Plan • Review Literature & Practices • Consider spacing increments • 600-ft • Evaluate spacing distances • Propose standards for Kentucky

  3. Spacing Principles • Mechanism for preserving functional integrity of roadway • Deviations are allowable • Signal spacing function of speed • Improve safety • Conflict points • Sight distance

  4. Spacing Principles (cont’d) • Variable spacing by AM class due to different • Priorities (mobility vs. accessibility) • Volumes • Design elements • Driver expectancies

  5. Interchange Spacing Signalized Spacing Non-Signalized Spacing Driveways Median use and openings U-turns Corner Clearance Management Techniques

  6. Interchange Spacing • Ramp separation to allow for merging & weaving • Important for fully controlled access roadways (interstates, freeways) • Possibly applicable to Principal Arterials • AASHTO guidelines • Urban 1 mile • Rural 2 miles

  7. Interchange Spacing (cont’d) • States with AM varied • OR Interstate U 3 mi/R 6 mi Expressway U 1.9 mi/R 3 mi • TX U 1 mi/R 2 mi • MO Interstate & Prin Art U 2mi/R 5 mi • FL CDB 1 mi/Non CDB 2 mi/SU 3 mi/R 6 mi • NCHRP 348 • Freeway U 1 mi/ R 3 mi • Expressway U 1 mi/R 2 mi

  8. KY Interchange Spacing

  9. Interchange Termini

  10. Distances to Termini • AASHTO • Adequate geometry • Appropriate access control • NCHRP 420 • State practices 100-700 ft U/300-1000 ft R • Access Management Manual • Varied by movement and control type

  11. KY Interchange Termini Note: Values are based on AM Manual

  12. b b Intersection Sight Distance KY “6 sec” rule: Distance b traveled in 6 sec at posted speed limit 2001 Green Book: Distance b for 7.5/6.5/6.5 sec

  13. b b Intersection Sight Distance For 55 mph posted speed KY 6 sec 484 ft SSD 495 ft ISD 610/530 ft DSD 865/980/1135 ft R SU U

  14. Signalized Spacing • Proper signal location can • provide for the orderly movement of traffic • increase traffic-handling capacity • reduce frequency, severity of some crashes • provide for continuous traffic movement

  15. Signalized Spacing (cont’d) Progression Speeds (mph) Source: AM Manual

  16. Signalized Spacing (cont’d) • Signals at rural areas • Maximum cycle times • Excessively long cycles lead to increased delay • 120 seconds max • Uniformity should be maintained

  17. Signalized Spacing (cont’d) • States with AM consistent • FL 2,640 ft/1,320 ft • MO 2,640 ft/1,320 ft (collectors); 1 mi R • MT 2,640 ft/1,320 ft • TX, NJ 2,640 ft

  18. KY Signal Spacing

  19. Non-Signalized Spacing • Safety • 40 acc/mi crash rate 2.1 greater than 10 acc/mi • Sight distances • AM class • Mobility • Location • HCM 0.25 mph free flow speed reduction/acc/mi • Overlapping and conflicting movements • Frequent right turn options • Egress capacity

  20. Non-Signalized Spacing (cont’d) • Focus on driveway frequency • Typically based on speed and sight distance • AM practices focus on driveway consolidation • Most common and complex access • Driveway permitting can • Reduce the number of crashes • Improve the operation of the roadway (LOS) • Improve site design

  21. Non-Signalized Spacing (cont’d) • Most states have some type of driveway control • Access spacing should be greater for • Higher access class roadways • Rural roadways • Roads with high speeds and high volumes • Land use can dictate spacing • Intersection sight distances should be met

  22. Non-Signalized Spacing (cont’d) Source: UK Research

  23. Non-Signalized Spacing (cont’d) • States with AM varied • OR Major Arterial 1,320 ft/660 ft Minor Arterial 660 ft Collector 660 ft/330 ft • MO U 660 ft/ 220ft; R1,320 ft/330 ft • FL >45 mph 1,320 ft/125 ft; <45 mph 660 ft/125 ft • OH based on speed limit 645 ft/155 ft • NCHRP 348 • Function of traffic generator, speed, and access class

  24. KY Non-Signalized Spacing 1 1,200 ft for roads with speed limit >45 mph

  25. Median Type & Opening Spacing • Important for • Pedestrian safety • Vehicular efficiency • Vehicular safety • Roadway aesthetics • Typically more important for high class roads • Opening types • Full • Directional

  26. Median Type & Opening Spacing (cont’d) • States with AM • No openings for high class roads • FL Median Handbook Dir 1,320 ft/660 ft; Full 2,640 ft • TX Dir 1,320 ft/330 ft; Full 2,640 ft/660 ft • MO U Dir 1,320 ft/660 ft; Full 2,640 ft/1,320 ft R Full 2,640 ft/1,320 ft Guidelines for type by functional class • NCHRP 348 • U 660 ft/330 ft • R 1,320 ft; SU 660 ft

  27. KY Median Recommendation 1 Recommended for multi-lane facilities

  28. Corner Clearance • Without proper corner clearances… • Through traffic blocked by vehicles waiting to turn into a driveway • Right or left turns into or out of a driveway (both on arterial and crossroad) are blocked • Driveway traffic is unable to enter left-turn lanes on arterial • Driveway exit movements are impacted by stopped vehicles in left-turn lanes

  29. Corner Clearance (cont’d) Intersection Physical Area Intersection Functional Area

  30. Major A B D C Corner Clearance (cont’d) • Most states with AM utilize non-signalized spacing • Special consideration and analysis may be essential

  31. KY Corner Clearance 1 Based on non-signalized spacing 2 1,200 ft for roads with speed limit >45 mph

  32. Spacing Standards

  33. Recommended Practices • Must consider spacing standards and sight distance • Evaluate warrants for existing signals that do not meet spacing standard • Encourage corner property access via lower class roadway • Consider median to eliminate left-turns if access must be on higher class roadway

  34. Recommended Practices • Locate access to corner properties as far from intersection as possible • Consolidate driveways of adjacent properties whenever feasible • Eliminate left-turn access within intersection influence area • Require studies for access permits within intersection influence area • Provide access to outparcels within development