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Sub-problem 1c - Page 2 of 9

ID# C101C02

Sub-problem 1c: Analysis of Future Conditions

Let's consider the answers to these questions.

What is the appropriate future year for this analysis? The appropriate horizon for a future year analysis depends on a number of factors. Often, an agency has a standard target year (based on a regional travel demand model) on the order of five, ten, or twenty years. Sometimes the horizon is selected based on the level and type of the investment under consideration. For a major freeway investment, twenty years is often used. For a new signal installation, ten years is often used. We will use a ten year horizon for this analysis.

Which default values should be used for this future analysis? While we can take field measurements to determine the appropriate input data and default values to use for the analysis of existing conditions, this is not possible for a future analysis. What we must do is to use the existing data as a guideline and then, based on what we know about the projected changes in traffic conditions and in the transportation system itself, make estimates of these future values.

For the analysis of future conditions at the intersection, we must also consider how to establish reasonable values for other critical analysis parameters. For an unsignalized intersection analysis, the additional critical parameters include peak hour factor, critical gap, follow up time, and heavy vehicle percentage. For a signalized intersection analysis, these critical parameters include arrival type, saturation flow rate, peak hour factor, and heavy vehicle percentage.

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