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Roundabouts - Coggle Diagram
Roundabouts
Design
6.2.1 Speed Management :
Entry- slow traffic to design speed in tte
Exit
Fastest Path
6.3 Size, Position &
Alignment of Approaches
6.3.2 Alignment of Approaches
6.3.1 Inscribed Circle Diameter
(150'-180' McKinney multilane)
6.3.3 Angle Between Approach Legs
Geometry
6.2.3 Appropriate Path Alignment
6.2.2 Lane Arrangements
6.2.4 Design Vehicle
6.5 Multilane Roundabouts
6.5.1 Lane Numbers and Arrangements
Need to have continuity between the entering, circulating, and exiting lanes such that lane changes are not needed to navigate the roundabout.
6.5.2 Entry Width
Two Lane 24' -30'
So, 12' - 15' per lane
Performance Checks
Fastest Path
R1,R3,R5 < 228'
R2,R4 < 296'
Design Vehicle (WB-67)
Sight Distance 6.7.3
At Entry Approach - both stopping & Intersection sight distance
Along circulatory Lanes - to crosswalks at exit approach
Visibility
Criteria
Local (city)
McKinney Street Design Requirements
subsection 2.3.E Roundabouts
National Cooperative Highway Research Program (NCHRP)
Report 672 Roundabouts: An Informational Guide
Principals and Objectives
Slow entry speeds & consistent speeds throughout by using deflection
achieve adequate capacity, lane volume balance, lane continuity
provide smooth channelization
provide adequate accommodation for the design vehicles
meet the needs of pedestrians and cyclists
provide appropriate sight distance and visibility for drivers and conflicting users