s51 multi-lane roundabout design ltc2013
DESCRIPTION
cccTRANSCRIPT
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MULTI-LANE
ROUNDABOUT
DESIGN
1
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HOW DOES A MULTI-LANE
ROUNDABOUT DESIGN DIFFER
FROM A SINGLE LANER?
2
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OLD FHWA Recommendations
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Offset Left Now Preferred
by Many Organizations
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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
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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
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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..
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Design Steps
4th – copy the
new center line
over 12’ for your
new right edge
line
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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…
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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
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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
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DOES
THIS
WORK?
Can you utilize
single lane design
techniques on 2
lane roundabouts?
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DOES
THIS
WORK?
NO
There is one critical
design error that
needs to be
addressed…
What is wrong?
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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
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Multi-Lane Roundabout Issues
Entry path overlap
Design vehicle tracking
On approach
Within circulatory roadway
Signing & Striping critical to achieve
desired lane use…
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Entry Path Overlap Example
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Which lane do I want to enter???
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Which lane would you likely enter???
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Offset Left Design Demonstrated
and Entry Path Overlap Eliminated
per NCHRP 672
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CAD Steps for 2 Laners
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CAD Steps for 2 Laners – Guestimating?
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CAD Steps for 2 Laners – 1 car length
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CAD Steps for 2 Laners – Tangents Done
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CAD Steps for 2 Laners – 6’ Offset Method
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CAD Steps for 2 Laners – Now 140’ +/- Fillets
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CAD Steps for 2 Laners – Almost Identical
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2 lane Approach Layout
we are now using 14 or 15’ wide lanes and a 4 or 6’ gore
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2 lane Approach Layout
Entry Path Overlap Check
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Improved Driver View From Yield Line
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Desired View From Yield Line
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What Can You Do If Already Built?
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Entry Path Overlap “Fixed” With Striping
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Entry Path Overlap FIXED! http://teachamerica.com/RAB11/RAB1109Vorisek/player.html
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What about a WB-67 Design Vehicle?
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MUTCD Path Overlap
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MUTCD Path Overlap –
What Happens to Red Car?
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Entry/Circulatory Roadway Tracking Truck Gore Striping was Implemented
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Left Approach Lane Tracking With Truck Gore Striping
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DOTD is recommending Case 2 Designs
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Anyone know how much over-tracking is OK
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Case 1 - Undesired Circulatory Track Every roundabout design should be checked for truck tracking
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Kingston Roundabout Striping
If you sign it like a single lane it will function as a single lane
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“Typical” 4 way intersection
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Slight Circular Adjustment
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Malta - Possible Moves
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Rt 67 at US 9 in Malta, NY
Trucks Turn Left from Right Lane – Why???
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Rt 67 at US 9 in Malta, NY
Cars Turn Left from Right Lane – Why???
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Latham Traffic Circle Retrofit - Before
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Latham Traffic Circle Retrofit - After
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Latham Multi Lane Approach – Before
Alignment, Signing & Striping
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Latham Multi Lane Approach – After
Alignment, Signing & Striping
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Latham Multi Lane Approach Signing
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NYSDOT Multi Lane Roundabout Signing
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NEW NYSDOT Multi Lane Signs
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NEW NYSDOT Multi Lane Arrow Placement
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NEW NYSDOT Multi Lane Arrow Placement
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NYSDOT 2 Lane Roundabout –
arrows still need to be moved
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RT. 9 @ RT. 67 ROUNDABOUT
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58
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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
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RT. 9 @ RT. 67 CRASH RATE –
Some changes worked
better than others
60
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YIELD “TO BOTH LANES” Signing
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Here is what we hope the new sign resolves
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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
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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
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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
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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
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METER NEEDED TO BE ADDED
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Thank you to Everyone
Here Today and
To All that Contributed
to this Conference