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Sub-problem 2d - Page 1 of 7

ID# C402D01

Sub-problem 2d: How Can We Improve the Level of Service at the Ramp Junction at the Northbound On-Ramp to I-87?

Step 1. Setup

The merge point that we considered in sub-problem 2c was over capacity during the PM peak hour. Queues extended over much of the length of the ramp. The demand exceeded capacity and the HCM methodology couldn't be used for this analysis under conditions present during the PM peak hour. But while the HCM methodology couldn't forecast the performance, we do know that the facility will fail since the demand was found to exceed capacity.

Consider how we could mitigate this problem. What possible changes in the design of the ramp merge area should be considered? To provide insight into possible geometric mitigations, we can look more closely at the forecast models. There are five variables of prime importance:

  1. Free flow speed on the ramp.

  2. Free flow speed on the mainline.

  3. Number of lanes on the ramp.

  4. Number of lanes on the mainline.

  5. Length of the acceleration lane in the merge area.

Many factors determine whether or not changing any of these variables is feasible. But we can use the HCM procedure to determine how much change we can expect in the operational performance if one or more of these variables is modified.

What possible design changes would you suggest to mitigate this problem? When you are ready, continue to the next page.

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