New Design Guidelines for Accommodating Trucks at Multilane Roundabouts

1. Purdue Road School March 9, 2011 Wes Butch DLZ Corporation New Design Guidelines for Accommodating Trucks at Multilane Roundabouts

2. Topics • Background Information • Scope of Study • Study Intersections • Design Characteristics • Field Observations • Crash Data • Trucking Industry Input • New Guidelines • Areas for Additional Study

3. Background Information • Accommodating trucks at multi-lane roundabouts (MLR) - debated since late 1990’s • Wisconsin DOT (WisDOT) • Aggressive and proactive roundabout program • Very active in freight issues/planning • Have an excellent Roundabout Design Guide • Interested in how trucks operate/best design practices for MLR’s • Partnered with Minnesota DOT (Mn/DOT) to perform study of trucks at MLR’s • DLZ is prime consultant for study team

4. Scope of Study • Definition of “Truck” • WB-65 in Wisconsin • WB-62 in Minnesota • Phase 1: Inventory/synthesis of current design practice • Phase 2: Targeted field data collection • Phase 3: Develop new design guidelines • Phase 4: Summary materials and information for commercial driver’s manuals

5. Scope of Study • Includes evaluation of: • Geometry • Operations • Crash data • Input from trucking industry throughout • Does not include oversize/overweight permitted loads • Technical Advisory Committee • NOT a statistically rigorous analysis of data (funding limitations) • Will recommend areas for further study

6. Study Intersections • Case 1: MLR where trucks overlap into adjacent lanes (~95%+ of MLRs built to date)

7. Study Intersections • Case 2: MLR where trucks stay in lane at entries, but overlap in circulating road/exits

8. Study Intersections • Case 3: MLR where trucks stay in lane throughout entire intersection

9. Study Intersections • Goal was to find 15-20 representative intersections for Phase 1 of study • Inventoried hundreds of intersections nationwide • Findings: • Case 1 roundabouts are everywhere • Case 2 roundabouts are concentrated in WI, AZ, NY, CA with smaller numbers in other states • Case 3 roundabouts are very rare (only two built that we could find)

10. Study Intersections • Case 1 intersections: • 4 in WI, 2 in MN, 1 in MI • Two are 3-lane, five are 2-lane • All are built • Case 2 intersections: • 5 in WI, 2 in AZ • Two are 3-lane, five are 2-lane • All are built • Case 3 intersections: • 1 in AZ, 3 in WI • All are 2-lane • Only two are built • 18 total intersections

11. Design Characteristics • Case 1: • Typically smaller diameter (140’ to 170’), entry widths, exit widths, entry radii • Sometimes smaller exit radii • Always included truck aprons in central island • Rarely included truck aprons on outside of entry radii • Common to have successive curves with relatively tight radii (approach, circulate, exit) • Circulating lane widths typically equal

12. Design Characteristics • Case 2: • Typically larger diameter (160’-200’), entry widths, exit widths, entry radii • Usually larger exit radii • Always included truck aprons in central island • Never included truck aprons on outside of entry radii • Approach curves typically larger and more sweeping • Rarely had successive curves with relatively tight radii (approach, circulate, exit) • Almost always have hatched common use area between lanes on approaches • Lane widths often unequal in circulating road

13. Design Characteristics • Case 3: • Larger diameter (180’-210’), entry widths, exit widths, entry radii • Larger exit radii and flat exits • Always included truck aprons in central island • Never included truck aprons on outside of entry radii • Approach curves larger and more sweeping • No successive curves with tight radii (approach, circulate, exit) • Have hatched common use area between lanes on approaches • Lane widths often unequal in circulating road

14. Field Observations • Not always correlation between truck volumes and design type • For Case 2 and Case 3 locations, trucks usually stay in lane where design allows • Trucks prefer not to use central island apron if they can avoid it • At Case 1 locations, truck trailers often mount curb on outside of entry radius

15. Field Observations – Case 1

16. Field Observations Video Observations at Case 2 Approaches Video Observations at Case 2 Circulatory Roadways

17. Crash Data • Not statistically rigorous analysis – general trends only • Compared to Case 1, Case 2 roundabouts appear to have lower percent of crashes that involve trucks • Truck crashes often side swipe • Not assessing increases in other crashes due to larger geometry at Case 2 and Case 3 locations • Representative split of truck/non-truck crashes

18. Crash Data • Case 1 locations

19. Crash Data • Case 2 locations

20. Trucking Industry Input • Survey questionnaire (great response) asking about preferences for signing, design types • Not surprisingly, many prefer Case 2 and Case 3 designs • Want better signing on approaches – stay in lane or encroach • Prefer to avoid aprons if possible • Surprisingly, liability issues not raised as major concern

21. New Design Guidelines • Phase 3 of Study • Done by Summer 2011 • Advice on when to use the three cases • Thresholds - Truck % or volumes? • Cost, safety, and ROW impacts will be consideration • Specific design techniques that are preferred for Case 2 and Case 3 designs • INDOT Guide currently allows all cases

22. Areas for Additional Study • Rigorous statistical analysis of data: • Do Case 1 locations have higher rate of truck crashes? • Do Case 1 locations have overall lower crash rates? • Any significant differences in severity between cases? • How do truck percentages relate to crash rates? • Do trucks drive Case 2 and Case 3 designs as intended under different traffic conditions?

23. Input is Welcome • WisDOT and Mn/DOT welcome input from other state DOT’s and stakeholders

24. Credits • Arizona DOT • Minnesota DOT • Wisconsin DOT • University of Wisconsin TOPS Lab • Roundabouts and Traffic Engineering, Inc.