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ID# C1OV001

Overview

Printable Version Printable Overview, Introduction, and Getting Started

This case study presents information on a decision that will be made by the Idaho Transportation Department regarding the operation of an intersection on U.S. Highway 95 within the City of Moscow, Idaho. The intersection is currently stop-sign controlled but consideration is being given to installing a traffic signal at the intersection. Click here to see what kinds of problems will be considered as part of this case study.

The case study includes six problems, each one illustrating some aspect of this decision:

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Problem 1 analyzes the intersection under both stop sign and signal control;

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Problem 2 addresses the effects of adjacent intersections as well as progression considerations;

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Problem 3 illustrates how to evaluate the intersection under oversaturated conditions, and also how to take account of a significant change in vehicle mix;

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Problem 4 addresses the issue of actuated control;

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Problem 5 suggests how to deal with an adjacent road segment that is neither an arterial nor a two-lane highway; and

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Problem 6 shows how a planning-level analysis might be conducted.

The purpose of each of the problems is to show how various traffic analysis tools that are contained in the Highway Capacity Manual can be applied to assist traffic analysts, engineers, planners and decision-makers in making sound investment decisions regarding the signalization decision. There are some situations where this amount of analysis would not be necessary in order to make an informed decision, but the issues presented herein should always be considered so as to assure the final decision is consistent with system performance objectives.

The problems in this case study focus on the chapters of the HCM that deal with interrupted flow facilities, either signalized or unsignalized intersections. After studying this material, you should be able to:

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Analyze the operation of signalized intersections, unsignalized intersections, and urban arterials using the HCM.

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Understand what input data are required and the assumptions that are commonly made regarding default values for the HCM procedures for these facilities.

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Know the appropriate kinds of analysis that should be undertaken for both existing facilities as well as future facilities or conditions, including the scope of a facility that should be included in an analysis.

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Understand the limitations of the HCM procedures and when it is appropriate to use other models or computational tools.

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Know how to reasonably interpret the results from an HCM analysis and how these results can be used to support a particular decision regarding a change to a transportation system.

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