CHAPTER 18 - HIERARCHY OF INTERSECTION CONTROL

CHAPTER 18 - HIERARCHY OF INTERSECTION CONTROL - Chapter 18...

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Chapter 18 Chapter 18 The Hierarchy of The Hierarchy of Intersection Intersection Control Control
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Key Issue: Avoidance of potential conflicts among vehicle movements and between vehicles and pedestrian movements 16 Xing Conflicts 8 Turning Conflicts 8 Ped Conflicts
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Intersection Control Options How much judgment can drivers safely exercise to avoid collisions? Three levels of control are available: Level 1 Passive Control: Basic Rules-of-the-Road Apply No control Guide signs only Warning signs w/ or w/o guide signs Level 2 Assignment of ROW to Major Street or Rotational ROW YIELD control Two-way STOP control Multiway STOP control Level 3 Positive Alternate Assignment of Exclusive ROW Traffic Signals (Two-Phase and Multiphase) Traffic Control Agent/Officer
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Basic Rules of the Road Key Requirement: Sufficient visibility to avoid conflicts. B A Collision Point b a d B d A d B -a d A - b Visibility Triangle at an Intersection
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From Similar Triangles: Thus, when the position of Vehicle A is known (d A ), the position of Vehicle B (d B ) when the drivers first can see each other may be computed as: a b d a d b A B - = - b d d a d A A B - =
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Two Ways to Insure Safety Using the Visibility Triangle Rule 1: At the point where both vehicles initially see each other, both must have at least one safe stopping distance to the collision point. Rule 2: From the point at which both vehicles initially see each other, Vehicle A must proceed 18 feet past the collision point in the same time as Vehicle B moves to a point 12 ft short of the collision point. Both vehicles travel at their approach speeds.
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RULE 2 ILLUSTRATED A B 18 ft 12 ft Line of Sight
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A Procedure for Evaluation the Safety of Operation Under Basic Rules of the Road 1. Assume that Vehicle A (minor street) is at one safe stopping distance from the collision point: 2. Determine where Vehicle B is located when it first becomes visible to Vehicle A: ( 29 G S t S d A A A 01 . 0 348 . 0 30 47 . 1 2 ± + = b d d a act d A A B - = ) (
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3. Using either Rule 1 or Rule 2, determined the minimum distance Vehicle B should be from the collision point. Rule 1: Rule 2: 4. If d B (act) < d B (min), the condition is not safe ( 29 G S t S d B B B 01 . 0 348 . 0 30 47 . 1 (min) 2 ± + = ( 29 12 18 (min) 47 . 1 12 47 . 1 18 + + = - = + A B A b B b A A S S d d S d S d
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An Example Are these sight lines sufficient to allow operation under basic rules of the road? F = 0.348 G = 0.0% t = 2.5 s 40 mph 40 mph 30 mph 42 ft 20 ft 12 ft 60 ft ONE WAY B C A F = 0.35 G = 0.0% t = 1.0 secs F = 0.348 G = 0.0% t = 2.5 s
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Testing the visibility between Vehicles A and B: Step 1 Step 2 Step 3 ( 29 ( 29 ( 29 ft R d ft R d ft act d ft d B B B A 0 . 298 12 30 40 18 5 . 196 ) 2 (min, 3 . 300 348 . 0 30 40 5 . 2 * 40 * 47 . 1 ) 1 (min, 4 . 25 42 5 . 196 5 . 196 * 20 ) ( 5 . 196 348 . 0 30 30 5 . 2 * 30 * 47 . 1 2 2 = + + = = + = = - = = + =
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Step 4 Since both rules result in a d B (min) which is
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CHAPTER 18 - HIERARCHY OF INTERSECTION CONTROL - Chapter 18...

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