Chapter 191 Chapter 19: Elements of Intersection Design and Layout Make an initial sizing of the intersection Make an initial sizing of the intersection Choose proper channelization design Choose proper channelization design Select proper alternatives to improve unsafe intersections Select proper alternatives to improve unsafe intersections Describe types of mounting signal heads Describe types of mounting signal heads Chapter objectives: By the end of this chapter the student will be able to: Whether signalized or unsignalized, the control measures implemented at an intersection must be synergistic with the design and layout of the intersection. Chapter 192 Whats discussed in this chapter includes techniques for: Determining the appropriate number and use of lanes at an intersection approach, Determining the appropriate number and use of lanes at an intersection approach, Channelization, Channelization, Right- and left-turn treatments, Right- and left-turn treatments, Special safety issues at intersections, Special safety issues at intersections, Location of intersection signs and signal displays. Location of intersection signs and signal displays. Chapter Intersection Design Objectives and Considerations 1. To ensure safety for all users, including drivers, passengers, pedestrians, bicyclists, and others 2. To promote efficient movement of all users (motorists, pedestrians, bicyclists, etc.) Two primary objectives for intersection design: Chapter 194 The elements considered: Human factors (approach speed, user expectancy, decision and reaction times, etc. Traffic considerations (appropriate capacity, distribution of vehicle types and turning movements, approach speeds, special treatments for transit vehicles, pedestrians, and bicycles) Physical elements (abutting properties, traffic movements generated by them, intersection angle, existence and location of traffic control devices, sight distances, specific geometric characteristics) Economic factors (cost of improvements, effects of improvements on the values of abutting properties, the effect of improvements on energy consumption Functional intersection area (operational intersection area including deceleration and acceleration zones as well as queuing areas) Chapter A Basic Starting Point: Sizing the Intersection (how many lanes do we need?) STOP or YIELD see chapter 16 STOP or YIELD see chapter 16 LT and RT lane considerations for Stop- or Yield-controlled intersections. LT and RT lane considerations for Stop- or Yield-controlled intersections Unsignalized intersections Assumptions: All through vehicles Capacity 80% of a lane Chapter Signalized intersections (see chapters 17 and 18) Check LT needs Determine proper phase sequence Determine critical movements Determine cycle length and split effective green time Assumptions: h = 2.6 sec/veh t L = 4 sec/phase Tab 19.3 Sample Prob. Chapter 197 Sample Problem VcVc Chapter Intersection Channelization Vehicle paths may be confined so that no more than two paths cross at any one point Vehicle paths may be confined so that no more than two paths cross at any one point The angles at which merging, diverging, or weaving movements occur may be controlled The angles at which merging, diverging, or weaving movements occur may be controlled Pavement area may be reduced, decreasing the tendency to wander and narrowing the area of conflict between vehicle paths Pavement area may be reduced, decreasing the tendency to wander and narrowing the area of conflict between vehicle paths Clear indications of proper vehicle paths may be provided Clear indications of proper vehicle paths may be provided Predominant movements may be given priority Predominant movements may be given priority Areas for pedestrian refuge may be provided Areas for pedestrian refuge may be provided Separate storage lanes may be provided to permit turning vehicles to wait clear of through traffic lanes Separate storage lanes may be provided to permit turning vehicles to wait clear of through traffic lanes Space may be provided for the mounting of traffic control devices in more visible locations Space may be provided for the mounting of traffic control devices in more visible locations Prohibited turns may be physically controlled Prohibited turns may be physically controlled Vehicle speeds may be somewhat reduced Vehicle speeds may be somewhat reduced General principles Chapter 199 Freedom & Bulldog Chapter 1910 Look at the examples shown in pages 545 and 547 and learn what you can do with channelization to provide safer and smoother turns Look at the examples shown in pages 545 and 547 and learn what you can do with channelization to provide safer and smoother turns Make certain a RT bay is not blocked by queued through vehicles. Queue length must be estimated. Otherwise the RT bay will be useless (but you see this example at many locations, e.g., the RT lane on Bulldog WB at Taco Bell; the LT lane on northbound on University Parkway at Brent Brown car dealership Make certain a RT bay is not blocked by queued through vehicles. Queue length must be estimated. Otherwise the RT bay will be useless (but you see this example at many locations, e.g., the RT lane on Bulldog WB at Taco Bell; the LT lane on northbound on University Parkway at Brent Brown car dealership Some examples and Channelizing right turns Chapter Special Situations at Intersections Intersections at skewed angles (Read carefully) Existing Potential realignment Alternative solution using channelization Realignment of 4-leg odd-angle intersection: Remember two intersections are created. Which one is better? Chapter T-intersections: Opportunities for creativity Layout and phasing Chapter Offset intersections Problems and solutions Chapter Special treatments for heavy LT movements Think of advantages and disadvantages of these Chapter 1915 Continuous flow intersection LT Lanes RT Lanes Chapter 1916 The Advantages of CFI Simulations using VISSIM traffic modeling software show that CFI outperforms conventional alternatives dramatically. In case after case, CFI produced extraordinary improvements in levels of service under existing traffic loads and reductions in average intersection delay of 90% or more. Simulations using VISSIM traffic modeling software show that CFI outperforms conventional alternatives dramatically. In case after case, CFI produced extraordinary improvements in levels of service under existing traffic loads and reductions in average intersection delay of 90% or more. Achieves significantly more capacity than conventional at-grade intersection designs. Achieves significantly more capacity than conventional at-grade intersection designs. Offers substantial savings over grade-separated alternatives while providing equal or better performance. Offers substantial savings over grade-separated alternatives while providing equal or better performance. Can be deployed in one-, two-, three-, and four-legged versions. Can be deployed in one-, two-, three-, and four-legged versions. Requires little more right-of-way than a conventional at-grade intersection. Requires little more right-of-way than a conventional at-grade intersection. Provides clear lines of sight, avoiding the visual barriers created by overpasses. Provides clear lines of sight, avoiding the visual barriers created by overpasses. Helps reduce pollution by reducing congestion. Helps reduce pollution by reducing congestion. Requires shorter construction time and less utility relocation. Requires shorter construction time and less utility relocation. Chapter 1917 Diverging Diamond Interchange American Fork Main St. Interchange proposed design. Chapter Street Hardware for Signalized Intersections At least one of the two required signal faces for the major movement must be located between 40 and 150 ft of the STOP line, unless the physical design of the intersection prevents it. At least one of the two required signal faces for the major movement must be located between 40 and 150 ft of the STOP line, unless the physical design of the intersection prevents it. All signal faces should be placed within a horizontal 20 angle around the centerline of the intersection approach (including exclusive left- and/or right-turn lanes) All signal faces should be placed within a horizontal 20 angle around the centerline of the intersection approach (including exclusive left- and/or right-turn lanes) Chapter 1919 All signal faces should be placed at mounting heights in conformance with MUTCD standards All signal faces should be placed at mounting heights in conformance with MUTCD standards X-axis related to street width Chapter 1920 Post-mounted Mast-mounted Chapter 1921 Cable-mounted flexible signal head arrangement