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Home My WebLink About4 Venessa Garza 16Introductions Dana Shumard Dana .Shumard@Kimley-Horn .com 17 Years of Experience Jeff Whitacre Jeff.Whitacre@Kimley-Horn.com 15 Years of Experience Kimley »>Horn Presents Brownbag #5 Roundabouts 101 Presenters: Sam Delmotte, P. E. Dana Shumard , P.E. Jeff Whitacre , P.E., PTOE, AICP Sam Delmotte Sam .Delmotte@Kimley-Horn .com 8 Years of Experience Friend ofTRB Roundabout Committee & Member of TexlTE Roundabout Committee I/ J.::>/ LU.!.::> 1 Brownbag Outline • General Roundabout Characteristics • Site Selection • Neighborhood Traffic Circles , Mini-Roundabouts, Single & Multi- Lane Roundabouts • Construction Details & Standards •Public Involvement 7/15/201 2 Circular Intersections Rotaries Signalized Traffic Circles Neighborhood Traffic Circles "-----/ "-----/ What is a Modern Roundabout? • A compact circular intersection in which traffic flows counter-clockwise around a center island • Entering traffic yields • Approaches are channelized to deflect traffic into a proper entry path • Designed to slow the speed of vehicles Modern Roundabouts "-----/ I /l':::J/ LUl~ 3 ·· .. ···· Entrance line ' ·' ·' · ... : Yield Control • Entry Speed Control • Yield on E nt ry Circulatory roadway Truck apron Key Features [] Yield Control [QJ Circulatory Roadway 7/15/201S 4 Circulatory Roadway Characteristcs Semi-Truck Path Deflected Entry Paths • Central island deflects vehicles from a straight path . • Fastest Path Speeds: Fastest Path Speeds Mini-Roundabout 15 -20 MPH Si ngle Lane Roundabout 20 -25 MPH 20-23 MPH (Preferred) Multi-Lane Roun dabout 25 -30 MPH 25 - 27 MPH (Preferred) Inscribed Circle .,....._ __ Diameter (ICD) Central Is land Bus or Small Truck l/l':J/LUl.':J 5 Splitter Islands • Used to separate , deflect, and control speeds • Characteristics • Highly Visible • Hardscape or Landscape • Curbed or Painted • 3 Inch Curbs • 6 FT Wide Preferable Truck Apron Used for Truck Traffic Characteristics Highly Visible 3 Inch Curbs Width Sized for Design Vehicle 10 -16 FT Standards 7/15/20E Splitter Island 6 Pedestrians & Bicycles • Crosswalks • Located From Yield Line • 20 FT Minimum • 25 FT Preferred • Curb Ramps • Pedestrian Refuge ·. • 6 FT Wide Medians/Splitter ls.lands • Bike Ramps (When Needed) I /l':J/ LUJ.!::i 7 Site Selection • General Location Site Selection • Add itional Selection Based on Size • Typical Traffic Volume and ICD Ranges • Roadway Classifications , Etc • Intersection Control Evaluation • Traffic , Safety, ROW, and Site Impact Analysis Site Considerations • Existing and Projected Traffic Volumes • Drainage Impacts •Right-of-Way Impacts • Widening vs Reconstruction Evaluation 7/15/2019 8 Optimum Site Locations • Speed transition locations. • Creating gateways into commercial or residential districts. • Along collector and arterial corridors. • Closely spaced intersections. • Skew, complex geometry, or more than four approaches. • Interchange and ramp terminals. Typical ICD Sizes and Daily Service Volumes • The diameters provided are for general gu idance (face to face of outside curb). • Capacities vary substantially depending on ente rin g traffic volumes and turning movements (circulating flow). Neighborhood Traffic Circle Mini-Roundabout Compact Single Lane Single Lane Multi-Lane: 2 (Dual)-Lane Roundabout Multi-Lan e: 3-Lane Roundabout I Typical ICD (FT) Less than 50 50-90 80-100 115-150 150-200 200 -250 Typical Daily Service Volume (VPD) Less Than Less than 15,000 Less Than 15,000 Less Than 25,000 25,000 -45,000 45,000 to 55,000 I /l~/ LUl:I 9 Roundabouts Based on Roadway Classifications • These are general guidelines and are subject to site specific analysis. Neighborhood Traffic Circle Mini-Roundabout Compact Single Lane Single Lane Multi-Lane: 2 (Dual)-Lane Roundabout Multi-Lane: 3-Lane Roundabout Roadway Classifications Local/Local Collector /Collector, Collector/Local, Local/Local Collector /Collector Collector /Col lector, Collector/ Arterial Collector/ Arterial, Arterial/ Arterial Arterial/ Arterial 7/15/201S 10 Intersection Control Evaluation • What is "ICE?" • Traffic Analysis • Safety & Cost Benefit Analysis What is "ICE?" • Intersection Control Evaluation = ICE • Considers more than just operations • Setting , Users , Cost , etc •Three Step Process • Screening • Preliminary Control Strategy Assessment • Conceptual Layout and Opinion of Probable Cost • Intended to provide consistent procedure to promote innovative thinking when considering control types I /l'::J/ LU.L~ 11 7/15/201S What is "ICE?" -Step 1 • Screening -Helps to identify which control types merit further consideration based on: • Project Location and Roadway Characteristics • Traffic Data • Warrant Studies • Design Vehicle and Design Speed • Safety What is "ICE?" -Step 2 •Preliminary Control Strategy Assessment-Further engineering analysis for control types recommended in Step 1 • Operational Analysis • Roundabout Performance • Safety Performance • Multimodal Accommodations • Benefit-Cost Analysis • Topographic , Utility, & Right-of-Way Impacts 12 What is "ICE?" -Step 3 • Conceptual Layout and Opinion of Probable Cost • Can range from layouts with OPCC 's to a detailed control strategy assessment where public engagement, in-depth cost and life cycle analysis , and more detailed traffic analyses are used to evaluate feasibility Traffic Analysis • Real limitation to capacity of a roundabout are circulating volumes • Tools for analysis • Sidra • Can analyze up to 3 lane roundabout • Better control over lane configurations • Synchro • Limited to dual lane roundabouts • Model struggles with high volumes I/ l'::J/ LU l.'::J 13 Benefit Considerations • Safety Benefits • Substantial reduct ion in fatal and injury crashes . • Operational Benefits • M in i, single , and m ulti-lane roundabouts have proven to reduce delays in comparison to all-way stop and signalized locations . • In addition , consi der reduction in person -hours of delay and reduced commercial vehicle delay throughout the day (not just peak hours). • Environmental Benefits Comparison of Typical ROW Needs: Roundabout vs Comparable Signalized !&!!!!!!! Intersection •=---:;-..:- ______________________________ .............. "/ ' ' r ' I ' ! // ~== ----------_/-----,, \, -I Si ngle Lane ""'-:.:';.= \ Ro unda bout vs -·.~-: Signal ,i~~~ "'-"-at lnterACtlon .----.... ""' ..... - ------- Dual Lane Rou ndabout vs Signa l .......... ·- Source: NC HRP 672 7/15/201~ 14 Roundabouts in Corridors • Intersections are typically the bottlenecks in urban road networks . • By providing better capacity at the intersection , we can build narrower roads to allow for other stree t features. • Signalized intersections require dedicated turn lanes with sufficient storage to avoid queue spillback into through traffic lanes. • Roundabouts can usually accommodate the same amount of traffic with no turn lanes and can be sized to limit the amount of additional space required . • Roundabouts can also provide better access management. Drivers can more easily U-turn at intersections which can reduce the ~mount of median openings needed for development. I I l.'J/ LUl.::1 15 Characteristics of a Neighborhood Traffic Circle • General Characteristics •Size: Generally Fits Within Existing Intersection • Recommend 13 ' Minimum Travel Lane • Design Vehicles : • Typically Standard Vehicles • Fire Truck and School Bus Max • Roadway Speeds : 30 MPH • Roadway Classification: Local or Neighborhood Streets •Applicable Locations • Traffic Calming , Not Capacity • xisting TWSC or AWSC Burleson - Neighborhood Traffic Circle 7/15/2019 16 Burleson - Neighborhood Traffic Circle • Summercrest and Thomas • Existing AWSC : • Metering Effect • Traffic Vo lumes/Queu ing Cause No Gaps • Traffic Circle Continuous Traffic Flow, • Grouped Cars Togethe r and A l lowed Gaps • Reduced Queuing at Intersections If .l.Jf LU.l.J 17 Mini - Roundabout • Improves Traffic Capacity and Speed Control • General Characteristics Size : • 50 -90 FT ICD Design Vehicles : • Fire Truck , School Bus , and SU Trucks • Larger ICD : WB-50 1: Cen~ island sized to provide deftection for oassenQef cars II Trucks may need to pass over central island Entrance line and splitter island def'ioed by inscribed drde dlameter or by swept path o f large~ Splitter Gland mountable Of' J)i/!li nted yeHow Hgure l :~~ah.11 es ofaM.nt Ro~1 FHWA I Mlnl·Roundabout. 7/15/201' 18 Mini - Roundabout • Fully Mountable Central Island • Min imal increase to existing footprint • Splitter islands to direct traffic • Yield Entry • Fastest Path Speeds : 15-20 MPH Site Selection of a Mini Roundabout • Traffic Volumes • Daily entering volumes will not exceed 15 ,000 vpd • Hourly entering volumes will not exceed 1,600 vph • Roadway Speeds: 35 MPH or Less • Roadway Classifications: Collector/Local or Local/Local ·Locations • Residential Areas • Rural Areas : Used as a Traffic Calming Measure • Truck Volume -3% or less eplacement for AWSC -Can significantly reduce delay I I .l'::J/ LU l.::1 19 Neighborhood Traffic Circle vs Mini-Roundabout Neighborhood Traffic Circle • Traffic calming measure • Typically built within existing intersection footprint • No Spl itter islan ds/Minimal to no deflection angle at approaches • Bus or Fire Truck la rgest vehicle • Central Island has landscape Mini Roundabout • Traffic control measure • Typically larger than traditional i nte rsection • Splitter islands to reduce speeds and channelize traffic entering • ICD , entry rad ii, and exit radi i are designed to accommodate larger trucks and buses . • Mountable truck apron & ce ntral island • Increases Ca pa city McAlister Road -Mini Roundabout 7/15/201~ 20 Burleson - McAlister Rd • Traditional Mini-Roundabout • Design • 80 ' ICD • Fully Mountable • Construct ion : • Cost: $465 ,000 • Duration : 6 Months (March 2019) Burleson McAlister Rd • Mini-Roundabout • 80 ' ICD I I l.-::1/ LU .l.:1 21 Fort Worth W. 7th Area • Design • Fully Mountable • Design Vehicle : BUS 40 • 50 ' ICD • 25 ' Island , 13 ' Circulating Lane • Construction • City Crews • -$30 ,000 7/15/201' 22 Fort Worth - W. 7th Area • Small m i ni-roundabout • 50 ' ICD I/ l':J/ LUl::1 23 Characteristics of a Single Lane Roundabout • Improves Traffic Capacity and Speed Control • General Characteristics • Size : • Compact Single Lane: 80 -100 FT ICD • Single Lane : 100 -150 FT ICD • Design Vehicles : • Standard : Fire Truck , School Bus , and SU Trucks • Larger ICD : WB-50 to WB-67 College Station - Greens Prairie Ranch • Compact Single Lane Roundabout • Residential Location • Design • 110 ' ICD • Truck Apron and Landscape Central Island • Des ign Vehicle : WB 40 1 o· wut. n-usc PAIH sec SHCC1 C-12 f'OR NOUNDABOUT OCTAi.. SIGHINO NiO STitlPfNC 7/15/201~ 24 Burleson - Arabella • Traditional Single Lane Roundabout • Open Field Location Adjacent to a Subdivision • Design • 140' ICD • Truck Apron and Landscape Central Island Fort Worth - Bonds Ranch & US 287 • Single Lane Roundabout • Asphalt W id ening and Overlay • US 287 Ramp Interchange • ROW Constraints • Design • 130 ' ICD • Truck Apron with Hardscape Central Island I/ J.'J/ LU.L::I 25 7/15/201 26 Characteristics of a Multi-Lane Roundabout • General Characteristics • Size : • General : 140 -180 FT ICD • Maximum: 200 FT (Can be larger depending on s ite condit ions) • Lane Configurations • Customizable • Dual or 3 Lane • Hybrids : Single/Dual , Single/Dual/3-Lane • Select the right size and lane configuration based on the traffic needs • Design Vehicles: • Standard : Fire Truck , School Bus , and WB-50 Larger ICD : WB-62 to WB-67 I I J.::J/ LU J.::1 27 College Station Jones-Butler • Dual/Single Lane Hybrid • Oval Shape to Accommodate Multiple Legs • Design • (2) 13 ' lanes • 5 Entries/Legs • Design Vehicle: WB-50 Fort Worth Heritage Trace • Dual/Single Lane Hybrid • Residential/Commercial Adjacent to 1-35 • Sonic , Charter School , and Subdivision • Design • (2) 13 ' lanes • Truck Apron with Landscape Central Island 7/15/201~ 28 Odessa - Grant Ave: Gateway Feature • Oblong Multi-Lane Roundabout • Gateway to Downtown • Design • (2) 13' lanes • 5 Entries Encouraging Pedestrian Activity with Crosswalks and Enhanced Island I/ J.'J/ LU .l:J 29 Fort Worth - Northern Cross • Dual Lane Roundabout • Industrial Area with High Truck Traffic • Case 2 Design • Not Recommended Anymore without a Significant Percent Truck Traffic • Design • 175 ' ICD 7/15/201 30 Fort Worth - Bonds Ranch Corridor • Phase 2 Roundabout • US 287 (Multi-Lane Roundabout) • Shire Meadow (Dual/Single Lane Hybrid) • Design • US 287 : 180' ICD • Shire Meadow: 160 ' ICD • Truck Apron with Landscape esign Vehicle : WB -67 I /l':J/ LU.l~ 31 Construction Details & Standards • Landscaping • Typical Section (View of Circulating Lanes) • Truck Apron • Curbs: Speed Control , Visibility • Color: Contrast with Pavement • Outside Curbs • Height (Speed Control) • Splitter Islands ·Jointing • • Signing/Marking •Minimum •Arrows • Lane Markings (Solid , Yield Line , Etc) ·Advised • Advanced Signing • Optional • Contrast Markings • LED RPMs or Reflective RP Ms Landscape Requirements • Central island landscaping is recommended to vary in height from 3.5' minimum to 6' maximum. • Speed thresholds • 35 MPH and above: nothing that is structurally significant (walls , trees , etc) • 35 MPH and less : Most landscaping is acceptable. Make sure to check SSD and think through any potential safety risks. • Maintain proper stopping sight distance when designing landscaping . 7 /15/201 ~ 32 Landscape Requirements • Typical Landscape Zones • Chapte r 9 , NCHRP 672 6 :1 Slope (Max .) Inscribed Circle Diameter Central Island Perimeter Landscape Zone Wi dth Va ries to Ensure Adequate Stopping Sight (6 ft [2 m] Minimum) 3.5 (Min .)¥- to 6' (Max.) Ground Elevation Splitter island rrypical) PROPOSED US 287 NB FRONTAGE RO ROUNDASOlJT TYPtCAL SECTION ~ ~ :~~.:ONSTRUCTION . FOR ILLUSTRATIVE PURPOSES ONLY. W:1··2' PROPOSED SHIRE lolENXIW OR ROUNDABOUT TYPICAL SECTION @ ~ :~.:ONSTRUCTION. FOR ILLUSTRATIVE PURPOSES ONLY. I/ J.'J/ LU..L:J Central island ; • :· l •• \' : • ~: •• : .:. .. , .·-·_,, .. , ... .. : . : . : . · .. ·· Inner central island landscaping Perimeter central islan d landscaping Approach and comer radii la ndscaping rrypical) Typical Section 33 --::...~-- :===-.-- -= :~ __ ,.,... DClMl."""-1.1.)1 00 =:===...--. .:~;;;:------=~.:: =:=:::...--· --u.a ~==--- ~ ....... ~ ...... -· -~ TS=J_+ Truck Apron Details 7/15/20 : 34 I I J.'J/ LU .l:J Public Involvement • Recommended • Format Options • Minimum Engagement @ • Evaluation Period (Prior to 30%) • Prelim Design • Before Construction • Presentation (Town Hall) • Stations (Open House ) • Combination • Office Hours • Discuss Traffic Contro l • Social Media • When Major TCP Shifts Occur • HOA/Neighborhood/Stakeholders • Before Opening • Tailor to S ituation • How to Drive • Materials • De sign Vehicle • Turn ing Movements • Flyers/Leave Behinds • V ideos 35 7/15/20: Available Resources • FHWA • NCHRP Report 672 -Roundabout Guide • AASHTO Green Book • TMUTCD -Pavement Marking & Signing • Roundabout Committees • TRB Roundabout Committee • TexlTE Roundabout Committee 36 Future Roundabout Brownbags • Safety, Site Benefits , and additional Site Evaluation • Intersection Control Evaluation Criteria • Accommodating Trucks • Case 1, Case 2 , and Case 3 Des ign · • Neighborhood Traffic Circle and Mini-Roundabout Geometry • Single Lane Geometry • Multi-Lane Geometry • • Traffic Control • Drainage & Grading • Signing and Marking • Landscape & Hardscape • Sight Distance • Construction Details & Standards • Design Checks • Public Involvement I/ l'.:J/ LUl.':J 37