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