MULTI-LANE ROUNDABOUT DESIGN 1 HOW DOES A MULTI-LANE ROUNDABOUT DESIGN DIFFER FROM A SINGLE LANER? 2 OLD FHWA Recommendations Offset Left Now Preferred by Many Organizations Design Steps 1ST – place 150’ diameter circle at center of existing intersection. All work being done at this point is with paint lines – curb lines are just offsets from the paint lines Design Steps 2nd – copy 150’ diameter circle parallel around 18’ or so twice – once for the travel lane and another time for the truck apron NOTE: later you will need to check with AutoTurn, AutoTrack or a similar program Design Steps 3rd – use a 300’ to 800’ fillet to tie the center line to the exit side of the truck apron and the left edge line to the outside of the roundabout – use the same radius to let CAD worry about the taper.. Design Steps 4th – copy the new center line over 12’ for your new right edge line Design Steps 5th – use a 90’ to 110’ fillet to tie in the approach. Use the same radius on both sides – let CAD take care of the taper… RESULT One leg is done – you now have an approach with geometry that requires vehicles to slow down before the yield line. This technique has 2 points of speed reduction – you have staged and staggered the speed reduction RADIAL This layout technique has only 1 point of speed reduction and it is at the pedestrian and circulating vehicle conflict area. Also, the driver does have a clear view into the roundabout DOES THIS WORK? Can you utilize single lane design techniques on 2 lane roundabouts? DOES THIS WORK? NO There is one critical design error that needs to be addressed… What is wrong? ENTRY PATH OVERLAP Think about the driver…. They get to the yield line – look left – then look straight ahead – they forget about the 100’ radius that they have just been following Multi-Lane Roundabout Issues . Entry path overlap . Design vehicle tracking . On approach . Within circulatory roadway . Signing & Striping critical to achieve desired lane use… Entry Path Overlap Example Which lane do I want to enter??? Which lane would you likely enter??? Offset Left Design Demonstrated and Entry Path Overlap Eliminated per NCHRP 672 CAD Steps for 2 Laners CAD Steps for 2 Laners – Guestimating? CAD Steps for 2 Laners – 1 car length CAD Steps for 2 Laners – Tangents Done CAD Steps for 2 Laners – 6’ Offset Method CAD Steps for 2 Laners – Now 140’ +/- Fillets CAD Steps for 2 Laners – Almost Identical 2 lane Approach Layout we are now using 14 or 15’ wide lanes and a 4 or 6’ gore 2 lane Approach Layout Entry Path Overlap Check Improved Driver View From Yield Line Desired View From Yield Line What Can You Do If Already Built? Entry Path Overlap “Fixed” With Striping Entry Path Overlap FIXED! http://teachamerica.com/RAB11/RAB1109Vorisek/player.html What about a WB-67 Design Vehicle? MUTCD Path Overlap MUTCD Path Overlap – What Happens to Red Car? Entry/Circulatory Roadway Tracking Truck Gore Striping was Implemented Left Approach Lane Tracking With Truck Gore Striping DOTD is recommending Case 2 Designs Anyone know how much over-tracking is OK Case 1 - Undesired Circulatory Track Every roundabout design should be checked for truck tracking Kingston Roundabout Striping If you sign it like a single lane it will function as a single lane “Typical” 4 way intersection Slight Circular Adjustment Malta - Possible Moves Rt 67 at US 9 in Malta, NY Trucks Turn Left from Right Lane – Why??? Rt 67 at US 9 in Malta, NY Cars Turn Left from Right Lane – Why??? Latham Traffic Circle Retrofit - Before Latham Traffic Circle Retrofit - After Latham Multi Lane Approach – Before Alignment, Signing & Striping Latham Multi Lane Approach – After Alignment, Signing & Striping Latham Multi Lane Approach Signing NYSDOT Multi Lane Roundabout Signing NEW NYSDOT Multi Lane Signs NEW NYSDOT Multi Lane Arrow Placement NEW NYSDOT Multi Lane Arrow Placement NYSDOT 2 Lane Roundabout – arrows still need to be moved RT. 9 @ RT. 67 ROUNDABOUT fghjdfjj 58 RT. 9 @ RT. 67 CRASH DIAGRAM PROBLEMS: 1) Lefts from right lane 2) Outer lane not yielding to inner circulating lane 3) Higher than desired approach speeds 4) Tight ROW led to small radial design with large entry radii 59 RT. 9 @ RT. 67 CRASH RATE – Some changes worked better than others 60 YIELD “TO BOTH LANES” Signing Here is what we hope the new sign resolves A CONCERN WITH RBT ANALYSIS • MOST PROGRAMS ASSUME AN AMOUNT OF “DOUBLING UP” OR “RUNNING SIDE BY SIDE” ― but what if 1 lane flares to 2 without much circulating flow in front of it ― to better balance delay between legs • WHEN TO CONSIDER A SIGNALIZED ROUNDABOUT? ― when 1 or more dominant legs have little delay but cause significant delay to minor approach • HOW DOES IT WORK? ― the signal stops the dominant leg – allowing minor leg to enter the roundabout • WHAT DOES IT LOOK LIKE? ― the following image is from Clearwater, FL SINGLE LANE FROM NORTH WITH HIGH VOLUME CAUSES DELAY ELSEWHERE ― the signal stops the dominant leg – allowing minor leg to enter the roundabout • WHAT DOES IT LOOK LIKE? ― the following image is from Clearwater, FL ADDITIONAL LANE FROM NORTH IMPROVES DELAY FOR OTHER LEGS??? ― the signal stops the dominant leg – allowing minor leg to enter the roundabout • WHAT DOES IT LOOK LIKE? ― the following image is from Clearwater, FL ADDITIONAL LANE FROM NORTH IMPROVES DELAY FOR OTHER LEGS??? ― the signal stops the dominant leg – allowing minor leg to enter the roundabout • WHAT DOES IT LOOK LIKE? ― the following image is from Clearwater, FL METER NEEDED TO BE ADDED Thank you to Everyone Here Today and To All that Contributed to this Conference .