Purdue Road School March 9, 2011 Wes Butch DLZ Corporation

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

 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

 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

 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

 Case 1: MLR where trucks overlap into adjacent lanes (~95%+ of MLRs built to date)

 Case 2: MLR where trucks stay in lane at entries, but overlap in circulating road/exits

 Case 3: MLR where trucks stay in lane throughout entire intersection

 Goal was to find 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)

 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

 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

 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

 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

 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

Video Observations at Case 2 Approaches Video Observations at Case 2 Circulatory Roadways

 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

 Case 1 locations

 Case 2 locations

 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

 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

 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?

 WisDOT and Mn/DOT welcome input from other state DOT’s and stakeholders

 Arizona DOT  Minnesota DOT  Wisconsin DOT  University of Wisconsin TOPS Lab  Roundabouts and Traffic Engineering, Inc.