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Problem 5: Interstate 87 Interchange

Problem 5: Interstate 87 Interchange. 5a: Freeway merges and diverges 5b:Route 146 weaving section 5c: Stop-controlled intersections. We will show how to apply the HCM procedures to study several different points within the interchange. Partial cloverleaf with 3 on-ramps and 3 off-ramps

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Problem 5: Interstate 87 Interchange

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  1. Problem 5: Interstate 87 Interchange • 5a: Freeway merges and diverges • 5b:Route 146 weaving section • 5c: Stop-controlled intersections We will show how to apply the HCM procedures to study several different points within the interchange.

  2. Partial cloverleaf with 3 on-ramps and 3 off-ramps SB there is: single-lane off-ramp (direct) leading to Route 146 W single-lane off-ramp (loop ramp) leading to Route 146 E double-lane on-ramp (semi-direct) for both WB and EB traffic on Rt 146 NB there is: Double-lane off-ramp. It expands to a triple-lane ramp then becomes 4 approach lanes (2 leading WB and 2 leading EB) single lane on-ramp (loop) from Route 146 EB single lane on-ramp (direct) from Route 146 WB Characteristics of the I-87 Interchange

  3. Observations? Sub-problem 5a: I-87 Interchange - Merges and Diverges on the Freeway What parameter defines level-of-service at a ramp junction? The density of vehicles within the ramp influence area. Where is the ramp influence area? It is the downstream/upstream area within 1,500 feet of the merge/diverge point, respectively, and includes the two right-most lanes.

  4. Single Lane Ramps How does this ramp perform? southbound-to-westbound off-ramp AM Existing condition: Freeway volume upstream = 3,751 vph Ramp volume = 437 vph The downstream off-ramp volume = 314 vph AM Without condition: Freeway volume upstream = 3,841 vph Ramp volume = 455 vph The downstream off-ramp volume = 326vph AM With condition: Freeway volume upstream = 3,851 vph Ramp volume = 565 vph The downstream off-ramp volume = 326vph LOS = C (all cases)

  5. Observations? Multiple Lane Ramps How would a second lane affect ramp performance? The densities for a single lane are more than twice that of a double lane ramp!!!

  6. Sub-problem 5b: I-87 Interchange: Route 146 Weaving Section In the HCM what are the input variables for analyzing weaving sections? • Type of weave (A, B, or C) • Length of the weaving section • Free-flow speed • Terrain • The 4 weaving volumes • Peak hour factor • Percent trucks • Percent recreational vehicles

  7. Performance of the Route 146 weaving section under a variety of conditions

  8. Prediction of Delays at the Terminus of the Southbound-to-Eastbound Off-ramp How realistic is it to assume a critical gap of 6.2 seconds for right-turning vehicles? These results are not consistent with field conditions, therefore the critical gap must be much shorter These results are closer to observed field conditions How realistic is it to assume a critical gap of 4.1 seconds for right-turning vehicles? It is necessary to use an accurate critical gap value!!!

  9. Sub-problem 5: I-87 Interchange – stop-controlled intersections What might be done to mitigate the LOS F predictions?

  10. What have we learned? • The interchange is adequate with the site-generated traffic, except for the SB-to-WB off-ramp and the WB left onto the SB on-ramp. • In the context of the HCM procedures, we’ve seen how a variety of methods can be used to explore the performance of specific locations within the interchange, including: • Merge and diverge analyses to the major ramp terminals • Weaving analysis of the EB section of highway between the two loop ramps • Use of the unsignalized intersection analysis methodology to assess the performance of two stop-controlled intersections

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