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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