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Roundabout Capacity Analysis

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Title: Roundabout Capacity Analysis


1
Roundabout Capacity Analysis
NEW YORK STATE DEPARTMENT OF
TRANSPORTATION
2
My, not necessarily NYSDOTs, opinion of most of
the commonly used programs throughout the US from
an actual user and reviewer perspective
3
Roundabout Capacity Software
  • SIDRA Intersection
  • RODEL / ARCADY
  • SYNCHRO 6, 7
  • Results of NCHRP 3-65, Report 572
  • VISSIM
  • PARAMICS

4
Two Types of Capacity Prediction Models
  • Empirical
  • RODEL or ARCADY
  • Based on field measurements, not theory
  • Capacity measured during at capacity operation
    in U.K.
  • Gap Theory
  • SIDRA, SYNCHRO, VISSIM, Paramics
  • Theoretical Capacity
  • Seeing is believing

Note They can give very different results
5
Single Lane FHWA Study
6
Dual (2) Lane FHWA Study programs still do not
agree
7
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 ?

8
SIDRA pre-Version 3
  • Concerns over high capacity predictions with low
    circulating flows can be resolved use 1.2
    Environment Factor

9
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

10
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

11
RODEL similar to ARCADY
  • 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/inde
    x.htm

12
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
13
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

14
Capacity of an Approach not lane by lane ?
15
Geometric Parameters
16
Effective Geometric Parameters
V Approach Roadway Width E Entry
Width L Effective Flare
Length D Inscribed Circle Diameter R
Entry Radius Phi Entry angle
17
RODEL ROundabout DELay
18
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
  • Cant really go from RODEL to CAD file
  • User error is common
  • Really need to understand design

19
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

20
RODEL ROundabout DELay Remember leg from
the north
21
RODEL Future Desires
  • To have better control over input widths a few
    organizations have already developed default
    geometric inputs

22
SYNCHRO / SimTraffic 6, 7
  • 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
  • Doesnt calculate L.O.S. based on delay
  • Will do most other intersections

23
SimTraffic 6 clip Multi-Lane Roundabout Think
about which lanes go where
24
SimTraffic 7 clip Multi-Lane Roundabout 3D
simulation goes a long way with convincing
decision makers John Q. Public
25
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 doesnt follow typical
    designs

26
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. Over-designs
    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/Multi-lane
    20Roundabouts20Supplement.pdf

27
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

28
NCHRP 3-65 Report 572 Single Laners
29
NCHRP 3-65 Report 572 Delay Queue
30
NCHRP 3-65 Report 572 Two Laners
31
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

32
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

33
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

34
VISSIM
  • 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

35
VISSIM showing signalized ped crossings

36
VISSIM Clip using Level 1 - 2000
37
VISSIM Clip shows overall improvements
38
VISSIM Clip using Level 2 - 3000 more
39
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.
40
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 isnt as refined as other programs
  • Time Consuming you need to watch the video
  • Constant updates especially when dealing with
    DOT software installation procedures

41
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

42
PARAMICS
  • 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

43
Paramics Clip costs around 12,000
44
Paramics Clip
45
PARAMICS arrows show allowed movements

46
PARAMICS like VISSIM will demonstrate Too
Fast Too Furious driving behavior

47
PARAMICS USER years ago anyway
  • More time consuming especially with
    non-traditional lane use within roundabout
  • Truck/car interaction can be challenging
  • Decent control of lane use within roundabout
  • PARAMICS REVIEWER
  • Output Data isnt as refined as other programs
  • Time Consuming you need to watch the video

48
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 ?

49
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

50
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 DONT REALLY MATTER AS LONG
AS IT IS A GOOD DESIGN ?
51
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
  • DONT EXCEED 1400 VPH AT THE CONFLICT POINT FOR A
    1 LANER

52
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
53
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
54
The NYSDOT Roundabout Design Unit would like to
thank everyone for their attention this morning
55
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 roundabouts_at_dot.state.ny.us
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