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Problem 4: Clifton Country Rd/Route 146 Intersection

Problem 4: Clifton Country Rd/Route 146 Intersection. The main question at this intersection will be: are geometric changes and/or adjustments in signal timing needed to accommodate the site-generated traffic? . Base Case Phasing and Volumes Analysis Plans Description of Analyses

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Problem 4: Clifton Country Rd/Route 146 Intersection

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  1. Problem 4: Clifton Country Rd/Route 146 Intersection The main question at this intersection will be: are geometric changes and/or adjustments in signal timing needed to accommodate the site-generated traffic? • Base Case Phasing and Volumes • Analysis Plans Description of Analyses • Overarching Issues • 4a: AM peak hour - Existing Conditions • 4b: PM peak hour - Existing Conditions • 4c: 2004 PM - With vs Without Conditions

  2. Characteristics of the Clifton Country Rd intersection • Fully actuated signaling • EB approach is 5 lanes wide (left, triple through & signalized right) • WB approach is 5 lanes wide (double left, double through & free right) • SB approach has 3 lanes (left, left/through, & right/through) • NB approach has 4 (double left, through & free right)

  3. 2 large shopping complexes on each side of intersection Major interchange with I-87 ~1/10 mile east of intersection

  4. Observations? High volumes in the PM Peak Highest volumes on EB & WB approaches

  5. Sub-problem 4a: Clifton Country Road AM peak hour - Existing Conditions AM existing conditions will be used to examine: • Lane utilization • Coordination • Lane group definitions

  6. Lane Utilization The EB through is the movement where it is most important to use the real lane utilization Why is that? The real lane utilization is so different from the HCM default

  7. Coordination What are the effects of changing the Arrival Type from 3 to 5? What if we assume the coordination is worse than random arrivals? Reduction in EB delays and queue length Significant increase in delay, which also means longer queues

  8. Lane Group Definitions • The HCM is capable of analyzing many different lane groupings: • exclusive lefts (one, two, three, etc. lanes) • shared left-and-through lanes • through lanes • shared right-and-through lanes • exclusive rights • But it cannot do lane-by-lane analyses, and there are some lane groups that it doesn’t accommodate easily

  9. Lane Group Definitions • The southbound approach has the following lane configuration: • left, left/through • through/right • The HCM doesn’t provide for an exclusive left-turn lane in conjunction with a left/through lane. So what do you do? Based on the analysis this approach seems to be consistent with field observations Two criteria must be satisfied: 1) the innermost lane gets as much use as the center lane and the outermost lane gets very little use. 2) the queue lengths on the innermost lane and center lane are about balanced.

  10. Sub-problem 4b: Clifton Country Road PM peak hour - Existing Conditions PM existing conditions will be used to examine: • Lost time • Demand vs. Volume • Right turns on red

  11. Lost Time Start-up lost time is the initial green time that is not effectively used due to the perception, reaction, and start-up times required by the lead vehicles. What is the HCM default for lost time? 2 seconds The number of seconds, after the yellow interval begins, that vehicles are still entering the intersection What is the extension of effective green time? What is the HCM default for the extension of effective green time? 2 seconds What are the effects of having both values the same? Different?

  12. Demand vs. Volume Intersection turning counts yield volumes, whereas arrival counts yield demand Congested intersections have demand/volume ratios > 1.0 during the peak hour. What happens when the ratio becomes larger than 1.0? Queues begin to form and grow when the demand to capacity (D/C) ratio is greater than 1.0. Queues begin to dissipate when the D/C ratio falls below 1.0.

  13. Demand vs. Volume What observations can be made for this intersection? High delays and fairly high v/c ratios Near capacity For the with-site condition, the D/C ratio should be checked; mitigation will probably be necessary if it exceeds 1.0

  14. Right Turns on Red For the EB approach 10% of the right turning vehicles turn on red For the WB approach all of them are expected to turn on red since there is a separate right-turn auxiliary lane & not much opposing traffic For the NB approach we assume as many vehicles turn right during phases 1 & 2 as WB lefts in a single lane (550/2) What observations can be made about right turns on red?

  15. Observations? Sub-problem 4c: Clifton Country Road 2004 PM - With vs. Without Conditions What can be done? What has been done here?

  16. Conclusions and Observations • This problem has explored a number of capacity modeling issues in the context of the Clifton Country Road intersection. • We examined time periods, the relationships among HCM methodologies, times to use other tools, and interpretation of results. • We examined lane groups and lost times. • We explored issues of queue spillback, feasibility of identified solutions, demand versus volume and right turns on red. • In the PM with-site condition, we focused on feedback the impacts of various assumptions about the future conditions and the tie between geometric changes and intersection performance.

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