May 17, 2012 - Item 13 - Streets and Freeways Subcommittee€¦ · •Circular Intersections •...

Modern Roundabouts Presentation to Streets and Freeways Subcommittee By Rock Miller, P.E.

Clearwater FL Roundabout

• Safety • Economy

• Operations and Maintenance

• Environmental Friendliness • Use of Space • Operational Characteristics • Aesthetics

Why Roundabouts?

• Yield on Entry • Priority to Circulating Vehicles • Low Circulating Speeds • Entry Deflection • Splitter Islands • Pedestrian Crossings • Central Island

Key Roundabout Features

Not a Roundabout

• Circular Intersections • Pre-Date Automobiles

• Rotary Intersections • Massachusetts and New Jersey • High Speeds, Safety Issues

• Traffic Signals (c. 1920) • U.S. largely abandons roundabouts as an everyday intersection tool

Roundabout History

One Less Rotary

• U.K. leads Efforts to develop Optimum Design Approaches (c. 1970) • Placed Yields on Entry Approaches

• France adopts UK Approach in 1984 • Builds 15,000 Roundabouts by 1997

• Additional Development Efforts in Australia • Healthy Competition among Designers

Modern Roundabout Perfected

• U.S. Travelers Abroad bring home tales of all the circular rarely-stop intersections

• A few expatriates push for rediscovery of roundabouts for the U.S. (c. 1990)

• A few experimental locations gather attention

A Good Idea Gets Out

One of the First in U.S.

Vail, CO

• Mountain Resorts of Colorado were Instrumental in Reemergence of Roundabouts in the U.S.

• 1000 Roundabouts constructed in the USA since 1990 • FHWA is Strong Supporter of Concept • Insurance Institute is Strong Advocate • Public Acceptance for Single Lane Roundabouts is Good • About 20 States now Require study of the roundabout

alternative for any intersection • Institute of Transportation Engineers (ITE) about to adopt

a “Should Consider” policy for roundabouts when any intersection is being studied

Emergence in the USA

Roundabout in Santa Monica

• 26th Street at Washington

• Reduction of Traffic Conflicts • Reduction of Speeds • Shallow Angle of Collision • Up to 80% Reduction in Injuries and Fatalities (vs. Signals) • 20-40% Reduction in All Crashes • Potential to Eliminate 1000’s of Deaths per Year

Roundabout Safety

Typical Roundabout Conversion

• The greatest risk to the continuing

reemergence and more widespread

use of roundabouts is poor design

Roundabout Design

Anything Wrong Here?

Is this a Roundabout?

• Long Beach Traffic Circle

• Difficult to Standardize • Not Cookbook

• Iterative Procedure • No two locations are ever quite the same

• More reliance upon Experience of Specialist Designer • Many specialists are available to help

Design Procedure

FHWA Design Procedure

Fastest Path

Natural Vehicle Paths

Truck Swept Paths

Entry Curves

• Analysis Software • RODEL

• UK Method • Outputs Geometric parameters • Under “Redevelopment”

• AA-SIDRA • Australian Method • Handles wider variation of Inputs

• Others

Roundabout Capacity

• Flow vs. Capacity of Circulating Roadway • Ability to Enter Circulating Roadway through Traffic Gaps • Total Approach Flows of 20-25,000 Vehicles will work for

most Single Lane Roundabouts

Capacity Principles

• Similar Benefits to Single Lane • More Difficult for Drivers • Likely to Experience Backlash • May Require Larger Intersection Area

Multi-Lane Roundabouts

Multi-Lane Roundabout

Multi-Lane Roundabout

Spiral Striping

• Very Difficult for Blind Pedestrians to Identify Traffic Gaps • Especially at Multi-Lane Sites • Also at High Volume Sites

• US Access Board has Proposed that Roundabouts should have Signalized Crossings at all Entries • Controversial, Unresolved

• Second Greatest Risk to more Usage

Issues for Sight Impaired Users

• Swindon, England

The Magic Roundabout

Downtown Roundabouts

Mini-Roundabout

Roundabout for Bicycle Boulevard

• Park at Vista Bike Boulevard, Long Beach

Bird Rock, La Jolla, San Diego

Carmel, Indiana, Home of 65 Roundabouts