3/3/06Michael Dixon1 CE 578 Highway Traffic Operations Freeways Merge Influence Areas

3/3/06Michael Dixon2 Objectives Estimate flow entering influence area Estimate capacity and determining LOS Special cases (next class)

3/3/06Michael Dixon3 Flow Entering Influence Area (V 12 ) V 12 = P FM * V F 4-lane freeways (P FM = 1.0) 6-lane freeways  more complex 8-lane and 10-lane freeways

3/3/06Michael Dixon4 Flow Entering Influence Area (V 12 ): Choosing the P FM Equation four-lane: P FM = 1.0 eight-lane: only one choice ten-lane: only one choice six-lane: See Exhibit 25-6

Flow Entering Influence Area (V 12 ): Choosing the P FM Equation 3/3/06Michael Dixon5

3/3/06Michael Dixon6 Flow Entering Influence Area (V 12 ): Choosing the P FM Equation (cont.) Only an issue for six-lane freeway sections On-ramps do not affect V 12 If only on-ramps are involved  Eq. 1 If an off-ramp is involved  calculate L EQ if L EQ < L up and/or L down then use Eq. 1

3/3/06Michael Dixon7 Steps for Evaluating a Merge Area Calculate the adjusted volumes (V R, V F, V D ) Step 1: Evaluate the equilibrium distance Step 2: Calculate P FM Step 3: Calculate V 12 Step 4: Calculate total flow entering merge area (V R12 )

3/3/06Michael Dixon8 Steps for Evaluating a Merge Area (cont.) Step 5: Capacity for downstream freeway segment (c 1 ) Step 6: Capacity for merge influence area (only if v/c for step 5 is less than 1)(Exhibit 25-7) Step 7: Determine the LOS of the influence area (only if v/c for step 5 is less than 1)

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3/3/06Michael Dixon10 Six-Lane Example: Conditions

3/3/06Michael Dixon11 Six-Lane Example: Step 1

3/3/06Michael Dixon12 Six-Lane Example: Step 2 and 3

3/3/06Michael Dixon13 Six-Lane Example: Step 4 and 5

3/3/06Michael Dixon14 Six-Lane Example: Step 6 and 7