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SPACING STANDARDS

Develop spacing standards for Kentucky roadways to preserve functional integrity, improve safety, and manage traffic efficiently. Consider variables such as sight distance, speeds, and access control. Review literature and propose innovative management techniques.

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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

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