Thinking Through Roundabouts

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Rodney Patrick
5 years ago
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1 Thinking Through Roundabouts Presented by: Scott Ritchie, P.E.

2 Thinking Roundabouts Roundabouts Gaining Ground (USA Today) Why American Drivers Should Learn To Love the Roundabout (Tom Vanderbilt) ADOT Embracing Roundabouts Planning of Rbt Corridors is Up Community Involvement & Acceptance is Up Growing Popularity = Everyone Trying One

3 Are We Improving? Knowledge Still Evolving In U.S. Better Designs for Trucks - ADOT Gen1 vs. Gen2 Better Differential Between Rural / Urban More Site Specific Shapes and Lane Configs RTE s ~400 Rbts in the U.S. (100+ in AZ) Still Learning & Evolving Gen1 vs. Gen2 Rbts Public s Basic knowledge is growing Yes, we are Improving, BUT Poor Designs Still Implemented!

4 Top 5 Deficiencies 1. Lack of Deflection (#1 Design Principle) 2. Size / Shape Not Site Specific / Optimized 3. Improper Lane Configurations 4. Truck Operations Dysfunctional 5. Lack of Design Experience / Expert Assistance (Not Reviewed by a Qualified Designer)

5 Design Deflection? Not Enough Deflection! Resultsi n High Crash Rates Image Courtesy: NYDOT

6 Good Deflection

7 Design Deflection? Too Much! Results in High Crash Rates JUST RIGHT!

8 Thinking Size/Shape Simple Size/Shape Mods Ellipse

9 Thinking Size/Shape Dropping a Lane with good deflection

10 Thinking Size / Shape Changing Sizes/Shapes Along Corridor

11 Oversized? 184

12 Thinking Size / Shape

13 Thinking Size/Shape

14 Thinking Lane Configs???

15 Thinking Lane Configs Poor Design More Issues Poor Design

16 Trade Offs Balance Between Capacity, Safety, Cost (Sustainable) Often Aims Conflict (Gov t: ROW/Capacity;Designer: Truck/Speed) Can Lead to Multiple Alternative Solutions Capacity Safety Your Project Here? Explore Objective Triangle for Optimum Trade-off Cost

17 Thinking Lane Configs

18 Interim Lane Config.

19 Ultimate Lane Config.

20 Interim & Ultimate Converting Dual Thru to Dual Left (Curb in Place!)

21 1 st Consecutive Dual Left Truck Bypass Route Consecutive Dual Lefts SB & WB = High Speeds NB = Downtown 25mph Trucks Accommodated (stay in lane in entry) Sound Design Principles Sustainable Design

22 Designing for Trucks In-Lane WB-67 Stays In Lane in Entry Inside Lane Outside Lane

23 Solution: Trucks in Lane

24 Solution: Trucks in Lane

25 2012 Nat l Truck Study DOT Team to Analyze Truck Operations Nationwide; Develop Truck Design Guidelines MLRs First of its kind in U.S. Includes Rbt Evaluations of: Geometry (top 20 designs) Operations Crash data Trucking Industry Input Technical Advisory Committee Focus on Largest Std Hwy Trucks OSOW not included

26 Define Case Types Case 1: Trucks overlap into adjacent lanes at MLRs (need both lanes to enter MLR) Case 1: How Most MLRs Were Built for the Past 2.5 Decades in North America

27 Define Case Types Case 2: MLR where trucks stay in lane within entry, but overlap in circulating road/exits - (Req d by some states now)

28 Define Case Types Case 3: MLR where trucks stay in lane through entire intersection (req d on some projects)

29 Case 1 Operations Trucks Cannot Stay in Lane Image Courtesy: WisDOT Image Courtesy: KSU Listserve Image Courtesy: KSU Listserve

30 Case 2 Operations Case 2: Allows trucks to stay in lane in entry Trucks use as designed! Image Courtesy: Google Maps

31 Case 3 Operations Case 3: Allows trucks to stay in lane through WB-67 in Inside Lane WB-67 in Outside Lane Small CID! Small ICD!

32 Crash Data: Case 1 Case 1 Truck Crashes ~ 40% AVG

33 Crash Data: Case 2 Case 2 Truck Crashes ~ 16% AVG Case 2 Truck Crashes 2.5 X LOWER than Case 1

34 Accommodating Trucks U.S. Sized Trucks need extra clearance (like no other!) Finding Capacity & Safety Issues are Prominent (Case 1) Cars Passing to the right of trucks straddling both entry lanes is common (Case 1) Trucks Inability to Occupy Both Lanes in Pk Hr (Case 1) We Can Do Better for Trucks

35 Both Rural & Urban

Can See Black Tire Marks of Vehicle Paths No Overlap!

36 Accommodating Trucks Above all, Must Maintain Good Design Principles even when accommodating for trucks! Can See Black Tire Marks of Vehicle Paths No Overlap! Balanced Design with Proper Speeds & Body Language while allowing for Truck Movements

37 Watch for Path Overlap Can See Black Tire Marks of Vehicle Paths Path Overlap! Poor Design

38 Good Lane Alignments

39 Got Help? PUBLIC ACCEPTANCE Matters! Don t Accept: It s Just a Circle = Roundabout Creativity & Experience Identify Solution Better solution from another designer? Design Should Be Unique to Achieve Safety & Capacity Check Composition (Does it Flow? How Will it Drive?) Both Holisticly and Details Require LOTS of Experience (50+MLR or Peer Rvw) Let s Build More Roundabouts!

40 Questions? Scott Ritchie, P.E. (928) Designing & Implementing Roundabouts Nationwide!

Holistic Design Counterclockwise or Facing Backward: (LT Arm & LT Leg Out) Left Brain Logical Sequential Rational Analytical Objective Looks at Parts!

41 Holistic Design Counterclockwise or Facing Backward: (LT Arm & LT Leg Out) Left Brain Logical Sequential Rational Analytical Objective Looks at Parts! Clockwise or Facing Forward: (RT Arm & RT Leg Out) Right Brain Holistic Intuitive Random Subjective Looks at Wholes! Holistic Designers Can See It BOTH Ways

42 Rotating Figure Exit to Play Video

GEOMETRIC PARAMETERS Affecting Capacity ICD 2

Single Lane Roundabouts Geometric Design in Context -Urban versus Rural 1 GEOMETRIC PARAMETERS Affecting Capacity ICD 2 Effective Geometry V = Approach Road half width 3 E = Entry Width L = Effective Flare