Transcript NE ROUNDABOUTS TRAINING HANDOUTS

NEW YORK STATE
DEPARTMENT OF TRANSPORTATION
Roundabout Capacity
Analysis
My, not necessarily
NYSDOT’s, opinion of most
of the commonly used
programs throughout the
US from an actual user and
reviewer perspective
Roundabout Capacity Software
 SIDRA Intersection
 RODEL / ARCADY
 SYNCHRO 6, 7
 Results of NCHRP 3-65, Report 572
 VISSIM
 PARAMICS
Two Types of Capacity Prediction Models
Gap Theory
Empirical
 SIDRA, SYNCHRO,
VISSIM, Paramics
 Theoretical Capacity
 “Seeing is believing”
 RODEL or ARCADY
 Based on field
measurements, not
theory
 Capacity measured
during “at capacity”
operation in U.K.
Note: They can give very different results
Single Lane FHWA Study
Dual (2) Lane FHWA Study –
programs still do not agree
SIDRA
 Developed in Australia
 Gap theory analysis
 Geometric parameters partially considered
 Used by about 80% of the country
 Does signals, most other intersections also
 Calculates emissions – CMAQ money… 
SIDRA – pre-Version 3
 Concerns over high capacity predictions
with low circulating flows can be resolved –
use 1.2 Environment Factor:
SIDRA USER
 Quite user friendly – quick & easy to follow
 Movement displays are nice for design reports
 Data easily extracted from results
SIDRA REVIEWER
 Lots of output to review
 Quite a few “defaults” can be altered to
manipulate results
 Really want actual file
 Some user error is possible
SIDRA – Future Desires
 To go from
a display that
gives general
movement
data:
to a display that gives
conflict totals per lane
crossing locations or
at least per lane on
approach & circulating
 Also, export displays
RODEL – similar to ARCADY
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Developed in Great Britain
Empirical analysis
Geometric parameters considered
Used by about 30% of the country
D.O.S. based
Metric Only
Only models roundabouts
RODEL 2 (Arcady 7) is here…  for info see:
http://teachamerica.com/RAB08/RAB08S5BJohnson/index.htm
Why Roundabouts Re-emerged
 Research on 35
geometric variations
 Many roundabouts
were rehabilitated
and new sites were
considered
 Follow up study
confirmed the
capacity prediction
equations were valid
TRL study test track (U.K.) - 1968
Empirical Model
 Strongly relates capacity to detailed
geometry
 Accidents also directly related to geometry
 Great tool for the design engineer
 Helps find the “optimum” geometry
Capacity of an Approach – not lane by lane… 
Geometric Parameters
Effective Geometric Parameters
V = Approach
Roadway
Width
E = Entry Width
L’ = Effective
Flare
Length
D = Inscribed
Circle Diameter
R = Entry Radius
Phi = Entry angle
RODEL = ROundabout DELay
RODEL USER
 User friendly – but need to understand design
 Instantly see results from geometric revisions
 1 input screen is all you need
RODEL REVIEWER
 1 screen capture is all you need
 No real “defaults” that can be altered to
manipulate results
 Can’t really go from RODEL to CAD file
 User error is common
 Really need to understand design
RODEL – Future Desires
 To be able to analyze lane by lane –
unbalanced lane use, assumption of
circulating lanes, and compounding lefts
cause questionable results currently
RODEL = ROundabout DELay
Remember leg from the north…
RODEL – Future Desires
 To have better control
over input widths –
a few organizations
have already
developed “default”
geometric inputs
SYNCHRO / SimTraffic 6, 7
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Uses HCM 2000 equations
Geometric parameters not considered
Compared to real sites?
Will only analyze single lane roundabouts
 SIM Traffic will simulate up to 4 laners
 Doesn’t calculate L.O.S. based on delay
 Will do most other intersections
SimTraffic 6 clip – Multi-Lane Roundabout
Think about which lanes go where…
SimTraffic 7 clip – Multi-Lane Roundabout
3D simulation goes a long way with
convincing decision makers & John Q. Public
SYNCHRO / SimTraffic USER
 User friendly for single laners
 Inputs very similar to that of other intersections
 Difficult to control lane use within roundabout
SYNCHRO / SimTraffic REVIEWER
 Lots of data in output – real worth???
 Single laners – you need to watch video
 Multi-Laners – really no good way to review
since lane use within roundabout doesn’t follow
typical designs
SYNCHRO / SimTraffic – Future Desires
 To have LOS based on delay – hopefully the
formulas from Report 572 will be incorporated.
Currently, good designs get poor LOS because
they use 60 to 80% of their capacity. Overdesigns are rewarded with better LOS based
on ICU…
 WHAT IS ICU?
 WHAT DOES “#” MEAN?
 WHAT DOES “~” MEAN?
 If you use Synchro to simulate multi-laners please
make sure you take the time to read:
http://www.trafficware.com/assets/pdfs/Multilane%20Roundabouts%20Supplement.pdf
NCHRP 3-65 – Report 572
 National Cooperative Highway Research Program –
Applying Roundabouts in the United States
 Initial project is done, see Report 572
 FHWA wanted “U.S. program”
 Equation is best fit to existing US conditions
 Multi-Lane analysis is based on critical lane
 Currently working on the next FHWA Roundabout
Guide
NCHRP 3-65 – Report 572 – Single Laners
NCHRP 3-65 – Report 572 – Delay & Queue
NCHRP 3-65 – Report 572 – Two Laners
NCHRP 3-65 - Report 572 USER
 User friendly – if you can work a calculator
 Easy to determine if capacity is there
 Delay & Queues require a little more time
NCHRP 3-65 - Report 572 REVIEWER
 Need to check lane assignments
 No “defaults” that can be altered to manipulate
results
 User error is eliminated
 Designer error can still influence results
NCHRP 3-65 – Report 572 – Future Desires
 To have a more user-friendly platform
 To be able to account for unbalanced
circulating flows
 To be able to analyze each approach lane
separately
 To be able to apply to 3 lane roundabouts
Simulation Programs
 Not typically used for roundabout design –
are being used to visually check predictions –
NYSDOT wants to see VISSIM
 Great tools for Public Info Meetings
 Able to show network impacts
 Visually displays improved performance
provided by roundabouts
 VISSIM seems to be more common choice
 Paramics is comparable but more expensive
VISSIM
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Developed in Germany
Gap Based – not geometric specific
Great tool for Public Info Meetings
Able to show network impacts
Can visualize impacts from signalized
pedestrian crossings… 
 Does nearly any roadway & intersection
configuration possible: like cfi, ddi, spui …
VISSIM – showing signalized ped crossings
VISSIM Clip – using Level 1 - $2000
VISSIM Clip – shows overall improvements
VISSIM Clip – using Level 2 - $3000 more
Using 3D Studio Max with VISSIM
This video comes from a project in Carmel, Indiana. You might
want to put in your paperwork now for the 2011 National
Roundabout Conference in Carmel – May 11-13th or so.
VISSIM USER
 More time consuming – unless using templates
 Truck/car interaction can be challenging
 Excellent control of lane use within roundabout
VISSIM REVIEWER
 Output Data isn’t as refined as other programs
 Time Consuming – you need to watch the video
 Constant updates – especially when dealing
with DOT software installation procedures
VISSIM – Future Desires
 To not have vehicles be able to cross through
each other – conflict areas???
NOTE: Make sure you never have vehicles
crossing in your presentation! We do not want
to go in front of the public with an actual
VISSIM file – video clips are much safer.
 Standardized “appealing” Output Format
PARAMICS
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Developed in Scotland
Does have actual roundabout “node”
Roundabout “node” does have limitations
Great tool for Public Info Meetings
Origin-Destination based routing
A little bit more expensive than the other
programs
 Steep learning curve
Paramics Clip – costs around $12,000
Paramics Clip
PARAMICS – arrows show allowed movements
PARAMICS – like VISSIM – will demonstrate
“Too Fast Too Furious” driving behavior
PARAMICS USER – years ago anyway
 More time consuming – especially with nontraditional lane use within roundabout
 Truck/car interaction can be challenging
 Decent control of lane use within roundabout
PARAMICS REVIEWER
 Output Data isn’t as refined as other programs
 Time Consuming – you need to watch the video
PARAMICS – Future Desires
 To not have vehicles be able to cross through
each other – does not go over well with less
than enthused audience
 Standardized “appealing” Output Format
 Large Vehicle tracking more realistic
 Better lane control at approach and within
roundabout – sometimes vehicles will realize
at the yield line that they needed to be in other
lane – could be realistic though… 
Roundabout Capacity Software
 SIDRA Intersection
 RODEL / ARCADY
 SYNCHRO 6, 7
 Results of NCHRP 3-65, Report 572
 VISSIM
 PARAMICS
 ANY OTHERS???
 Which one (or more) to choose???
 The next few slides show a “simplified” method
used at NYSDOT
The Real Limitation to the Capacity of a
Roundabout is at the Yield Line
The availability of usable
gaps in the circulatory
roadway traffic for
approaching vehicles trying
to enter the roundabout is
what truly limits the
roundabouts capacity…
THE ACTUAL DESIGN
SPECS DON’T REALLY
MATTER AS LONG AS IT
IS A GOOD DESIGN… 
Quick Capacity “Guesstimate” for
Single Laner
 0 - 750
LOS A
 750 - 850
LOS A / B
 850 - 950
LOS B / C
 950 - 1050
LOS C / D
 1050 - 1150
LOS D / E
 1150 - 1400
LOS E / F
 DON’T EXCEED 1400 VPH AT THE
CONFLICT POINT FOR A 1 LANER
Capacity Limits Not Lane by Lane
If sum is 0 – 1,000 then
Single lane works
If sum is 1,000 – 1,300 then
Single lane might work
If sum is 1,300 – 1,800 then
2 laner works
If sum is1,800 – 2,200 then
2 laner might work
If sum is 2,200 – 2,900
3 laner might work
Capacity Limits –Still want to Check Lane
by Lane – now 900 vphpl is limit
The 1,000 rule of
thumb drops to 900
because entering
vehicles need to find
acceptable gaps in
both circulating lanes
at once – some gaps
in the outer lane will
be eliminated by the
vehicles circulating in
the inner lane….
Potential
Capacity
Problems
The NYSDOT
Roundabout Design Unit
would like to thank everyone
for their attention this
morning…
NYSDOT Roundabout Design Unit
Contact Information
Howard McCulloch, Richard Schell, PE
Michael Houlihan, Greg Bailey
and Tom Kligerman, PE
Roundabout Design Unit
50 Wolf Road, POD 24
Albany, New York 12232
Tel: (518) 485-7503
Fax: (518) 457-2916
E-mail: [email protected]