1. Roundabout Feasibility: Analysis Framework and Design Considerations Presented By: Jason D. Pack, P.E. Fred Choa, P.E.

2. Presentation Overview Roundabout Planning – When should you consider? Roundabout Operations Roundabout Analysis Methods & Software Roundabout Analysis Framework Case Study #1 – SR 32 in Chico, CA Case Study #2 – Kietzke Lane in Reno, NV Roundabout Design Feasibility Considerations Takeaways and Resources

3. Roundabout Planning Capacity (e.g. LOS D/E) – Our Experience Single-Lane Roundabout – 20,000 ADT Capacity Two-lane Roundabout – 35,000 ADT Capacity Note: These are general and are for planning purposes only Be careful with high peaking uses like schools As soon as a queue extends to a roundabout, the entire system breaks down Grade – Roundabouts should not be implemented on grades greater than 6%

4. Roundabout Planning In General: Roundabouts work wherever you are considering an all-way stop Roundabouts usually work if you were considering a “typical” signalized intersection If you are considering multiple turn lanes at an intersection, roundabout feasibility becomes questionable Use the series of checks and framework to ensure it will work

5. Roundabout Planning When Should You Consider a Roundabout? Source: NCHRP 672

6. Roundabout Planning Number of Entry Lanes

7. Analysis Methods Macroscopic Models For isolated locations Analyze vehicle flows HCM 2010, FHWA, RODEL, SIDRA, etc. Microscopic Models For system analyses Analyze individual vehicles & drivers SimTraffic, Paramics, & VISSIM

8. Analysis Software FHWA & RODEL Based on British regression equations Gap acceptance & lane configuration are not addressed in the calculation Very easy to use SIDRA & SimTraffic Allow calibration of gap acceptance parameters to local conditions Easy to use Paramics & VISSIM Most flexible in modeling driver behavior More difficult to use as there are more parameters affecting driver behavior

9. Analysis Framework

10. Case Study #1 Widening of SR 32 in Chico, CA Two-lane rural highway with access control Design Year (2030) PM Peak Hour Project considered roundabouts at the 4 study intersections

11. Study Area

12. Proposed Design Source: Mark Thomas & Co.

13. FHWA Guidelines ADT on SR 32 & Bruce Road at the limit Daily volumes on Bruce Road are above 40,000 vpd with high left-turn percentages Peak-hour volumes exceed entry & circulatory volume capacity Entry + circulatory flow ~ 2,500 vph Both indicate that the roundabout should be at or over capacity – simulation recommended….

14. VISSIM Results: LOS F

15. Macroscopic Analysis What happens if we don’t follow the framework and evaluate the roundabout with macroscopic analysis? RODEL SIDRA

16. RODEL Results: LOS A

17. SIDRA Results: LOS C

18. Review of RODEL Results 20% increase in volume yields LOS F RODEL manual does not identify the upper limit of the empirical data RODEL does not account for right-turn delay even if vehicle queues block access to bypass lanes RODEL does not consider the capacity of the circulatory roadway

19. Review of SIDRA Results V/C Ratios on all approaches exceed 0.85 95 th percentile queue is 883 feet

20. Review of VISSIM Results Insufficient Circulatory Capacity Blocked Right-turn Bypass Lanes

21. Case Study #2 – Reno, NV Initial study performed using RODEL Applied framework and realized that microscopic assessment was required due to system analysis

22. Study Area Proposed Roundabout Location

23. Proposed Design Results Southbound queue as long as existing queue with all-way-stop Northbound vehicles will experience long queues and delay

24. Roundabout Feasibility Source: NCHRP 672 Key Terminologies

25. Roundabout Feasibility – Inscribed Diameter Single Lane Roundabout – 110’ to 180’ Two Lane Roundabout – 150’ to 220’ Three Lane Roundabout – 200’ to 300’

26. Roundabout Feasibility Design Vehicle: Single Lane Roundabout – 110’ to 180’  110’ to 120’ Single-Unit Truck (SU)/Bus  120’ to 150’ SU, Bus, and WB-50  150’ to 180’ SU, Bus, WB-50, and WB-67 Two Lane Roundabout – 150’ to 220’  150’ to 220’ WB-50  165’ to 220’ WB-67 Source: NCHRP 672

27. Elements of a Well Designed Roundabout Deflection – prior to yield line No entry and exit path overlap Smooth and consistent entries and exits Advanced signing that clearly shows lane destinations to facilitate lane selection prior to entering the roundabout Striping and pavement markings which guide drivers to their intended destination Lighting that positively lights a pedestrian within the crosswalk

28. Typical Splitter Island: Source: NCHRP 672

29. Fastest Paths and Approach Speeds: Fastest path speeds at all entries need to be balanced Entering and circulating speeds are separated by less than 12 mph (8 mph desirable) R 1 speed for all approaches should be within 5 mph of each other R 1 and R 4 should be within 12 mph of each other Speeds for R 2, R 3 and R 5 are not necessary

30. Path Overlap

32. Basic Principles of Roundabout Signing and Striping: Position vehicle in proper lane in advance of the roundabout Discourages lane changing in roundabout Identify proper turning movements in lanes Identify right-of-way

33. Bicycle Considerations: Speed at entries and circulatory roadway are lower (17 – 25 mph) Bikes can share roadway with vehicles on single lane roundabouts Separate bicycle path or shared bicycle- pedestrian path is preferred at multilane roundabouts

34. Consequences of Poor Design:

35. Consequences of Design:

36. Takeaways and Resources Utilize the framework to assist in understanding the limits of your analysis software and know whether you should be considering a roundabout Know your resources related to roundabout layouts/ feasibility MUTCD – Design Requirements FHWA – Roundabouts: An Informational Guide WSDOT Design Manual – Great Design Guide