Post on 22-Dec-2015
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CE 578 Highway Traffic Operations
Lecture 21: Freeway Ramps and Ramp Junctions Diverge Areas
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Objectives
• Basic concepts
• Important variables
• Relate to merge areas
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Basic Concepts
• Volume v12
• Capacities– Total departing– Prior to deceleration lane– Downstream legs
• Determine influence area flow density
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Important Variables
• LD
• VR
• VD
• VU
• V12
• VF
• VFO
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Important Variables (cont.)
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Important Variables (cont.)
VRVUVD
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Relation to Merge Area Procedure
• Estimate V12 using V12 = VR + (VF – VR)*PFD
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Ramp Sequence Scenarios
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Ramp Sequence Scenarios (cont.)
• Ramps with no affect---
• Upstream on-ramp:
• Downstream off-ramp:
• Both Upstream on-ramp and Downstream off-ramp:
• Use for LEQ of upstream on-ramp
• Use for LEQ of downstream off-ramp
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Capacity Comparisons
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Capacity Comparisons (cont.)
• Estimate and compare capacities (___________________________)
– Maximum flow that can depart (upstream mainline capacity (___________)
– Maximum upstream flow in lanes 1 and 2 prior to deceleration lane (___________)
– Maximum flow on downstream lanes• (______________)
• (______________)
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Determining LOS
• Calculate diverge area density: DR = 4.252 + 0.0086v12 – 0.009LD
• Use same LOS table