Module 4

The Roundabout and Intersection Operations

How efficiently does a roundabout perform?

Roundabouts in the United States

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

The Goal of Operational Analysis

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Roundabouts in the United States Module 4 — Roundabout Intersection Operations

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Intersection Operations Analysis

Data Collection

Traffic Volumes

ca p a c i ty G eom etr y

CONTROL

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Turning Movements

Land Use Planning

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

What Are the Goals of Intersection Design?

STOP

STOP

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Delay of Traffic at an Intersection

Control Delay

Geometric Delay

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Signalized Intersection Control

In a signalized system, some cars must come to a complete stop

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Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Systems that promote smooth flow of traffic are generally preferred

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Complex Systems Control Flow Through Signalized Corridors

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Photo: Peter Koonce

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

And signals will always cause some traffic to stop.

2:00 AM

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Roundabouts Are Self-regulating.

2:00 AM

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Roundabouts Operate Using a Gap-acceptance Process.

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Roundabouts Often Have Less Delay Than Signals

Based on MUTCD Warrant 3 (2000 ed.)/Warrant 11 (1988 ed.)

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Roundabout (10% left turns)

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MUTCD Signal Warrant Volume Threshold

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Roundabouts in the United States Module 4 — Roundabout Intersection Operations

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The Yield-controlled Intersection

Salt Lake City transportation official Tim Harpst likes the fact that traffic keeps flowing through roundabouts without a lot of stopping and starting. “They are not air-pollution causing. And you don’t have a traffic signal you have to maintain.”

The Salt Lake Tribune, December 26, 2002

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Reducing Delay, Increasing Free Flow

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Geometric Control: Right-in, Right-out

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

A Roundabout Operates Much the Same Way

Roundabouts in the United States Module 4 — Roundabout Intersection Operations

Roundabouts Can Also Be Incorporated into Diamond Interchanges.

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Roundabout Intersection Operations

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