Transcript VISSIM and Mn/DOT’s INTERSECTION CONTROL EVALUATION (ICE) VISSIM USER’S GROUP MEETING

VISSIM and Mn/DOT’s
INTERSECTION CONTROL
EVALUATION (ICE)
VISSIM USER’S GROUP MEETING
MAY 15-16, 2008
Philadelphia
Dennis Eyler, P.E., P.T.O.E.
Leif Garness, E.I.T.
Vice President
Traffic Engineer
SRF Consulting Group, Inc.
SRF Consulting Group, Inc.
[email protected]
[email protected]
Presentation Overview
• What is ICE?
• Issues with ICE
• Two examples of ICE for roundabout projects
 Old US 12 at Wayzata Boulevard
 Mn Hwy 22 and Blue Earth County 90
• Lessons learned
 Using VISSIM for roundabouts
 Roundabout Design
ICE OVERVIEW
ICE – Definition and Goals
• Creates standard analysis for Mn/DOT intersections
 Select geometry and traffic control early during project
development
 Encourage considering other forms of intersection
geometry and traffic control
 However, default is side street STOP control
 Anything else must be evaluated and “proven”
• Evaluate viable alternatives for:
 Safety
 Peak hour capacity
 Efficiency through all traffic levels
• Document selection reasons
 To avoid re-visits later in the project
ICE Flow Diagram
Intersection Alternatives
• Standard intersections
 Mn/DOT minimum for
signals
• 3 lanes (L-T-R) in, 1
lane out
• Quadrant roadways
• Michigan U (left) -turns
Continuous flow or lefts
in advance
• Roundabouts
• Jug handle
• One way pairs
• Through-about
• Offset “T’s”
• Super street
• Reduced conflict
• Double cross-over
At-grade Intersection Alternatives
Indirect or
“Michigan”
No left
turns
U (left) turns
No left
turns
Quadrant
intersection
CFI
Continuous
flow
intersection
Patented by F. Mier
Jug handle
Through about
SRF – Planning Level Evaluation
• Reduce alternatives early
• Evaluate alternatives quickly and efficiently by using
planning-level analysis
 Volume to capacity (V/C) determined by critical lane
 Performance impacts from look-up tables
• SRF spreadsheet intersection evaluation tool
SRF Intersection Evaluation Tool
Traffic Volume Input Sheet
Intersection Alternatives - Worksheet
Results are
V/C ratios
Right turn
bypass?
Number of
lanes
ISSUES WITH ICE AND
WARRANTS
Intersections - Warrants - Issues
• Warrants - guidelines for installing traffic control
devices:
 All-way stops
 Signals
• However, what are the warrants for intersection
geometry?
 Roadway system issues
• Hierarchy of intersecting roadways
• Corridor consistency
• Performance goals
 Costs versus needed level of control and capacity
• What if?
 Warrants for traffic controls are not met for 10 years
 But policy requires intersection design for 20 year forecasts?
Warrant Status
• Are warrants met?
 Traffic signal
 All-way stop
• Roundabouts
 Warrants? – (Mn/DOT criteria only if all-way stops or signals
are warranted)
• If not, will warrants be met by design year?
• When will warrants be met?
• What is interim solution?
 A roundabout is an intersection traffic control device
 Roundabouts are built as roadways
 What if warrants are not met in year of opening?
The BIG Question
• What do you build now if a roundabout is
the proper solution for the 20 year forecasts,
but the roundabout “warrants” are not met?
• The answer is to then “justify” the
roundabout
 Show that there is no safety issue
 Show that there are no capacity or efficiency
issues during the interim until warrants are
met
Controls and Travel Time
• VISSIM was selected by Mn/DOT as the best tool for
alternatives evaluation
 Obtain total travel time - from free flow in to free flow
out
 Queuing
 Delay
 Stops
• Evaluation of geometric features
 Capacity versus intersection geometry
 Also:
•
•
•
•
Turn lane lengths
Downstream merge distances
Vehicle tracking
Decision distance
• Effects of higher approach speeds and vehicle mix
Controls and Travel Time
Traffic control impacts total travel time
1.
Lengthening of path (e.g. downstream u-turn)
2.
Path geometry (e.g. slowing to use a roundabout)
3.
Control device delay (e.g. STOP sign)
4.
Control delay and impacts from sharing
intersection with other traffic
5.

Roundabouts – waiting to enter

Signals – waiting for green

All-way stops – waiting for turn

Side street stops – waiting for gap
Congestion delay to other traffic going in the same
direction (e.g. queue discharge or following a truck)
Added Travel Time(1) Due to
Major Speed Changes
• CARS
• TRUCKS
• Stop sign
• Stop sign
 35 to 0 to 35 = 14.2 secs
 65 to 0 to 65 = 24.4 secs
 35 to 0 to 35 = 19.7 secs
 65 to 0 to 65 = 45.0 secs
• Roundabout - 15 mph (2)
• Roundabout - 15 mph (2)
 35 to 15 to 35 = 9.1 secs
 65 to 15 to 65 = 18.6 secs
 35 to 15 to 35 = 20.7 secs
 65 to 15 to 65 = 46.8 secs
(1)
Compared to traveling at steady speed
(2)
Design speed of roundabout
(3)
Includes added travel time for distance in roundabout, but not delay due to other traffic
Travel time “trap”
Collect total travel time
for all vehicles from
approaching at free flow
speed to returning to free
flow speed
free flow
Project Examples
Project Examples
North
• Old US Hwy 12 in Orono, Minnesota
• Mn Hwy 22 at Blue Earth Co Rd 90 – south
east of Mankato, Minnesota
Project Location
Project Location
Old US 12 at Wayzata Boulevard
Close access
Add frontage roads
Construct roundabout
New US 12 freeway
Alternatives
Old Hwy 12 - Project Issues
• Prove that a roundabout is “justified”
• Prove that it won’t back traffic onto freeway
• Document the benefits
• Determine the required design for existing
conditions and for 20 years of traffic growth
Old US 12 – Results – 2008 volumes
Delay Summary (2008)
Type of Control
Approach
Move
Peak hour
STOP sign
Round-about
EB old TH 12
Through
AM
1.3
5.4
PM
0.6
0.7
AM
2.3
2.2
PM
5.5
0.1
AM
0.4
1.0
PM
0.9
3.6
AM
1.4
2.7
PM
1.4
4.2
AM
7.2
0.2
PM
19.7
10.8
AM
32.8
1.7
PM
15.3
21.1
AM
14.8
15.2
PM
55.1
27.2
Left
WB old TH 12
Through
Right
Wayzata Boulevard
Right
Left
Montessori Right Turns onto WB old TH 12
Old US 12 – Results – 2028 volumes
Delay Summary (2028)
Type of Control
Approach
Move
Peak hour
STOP sign
Round-about (1.5)
EB old TH 12
Through
AM
1.8
5.0
PM
0.7
1.3
AM
3.3
2.4
PM
13.6
1.7
AM
0.5
1.3
PM
1.4
4.0
AM
1.4
1.0
PM
1.6
2.9
AM
19.4
1.9
PM
229
36.2
AM
75.6
6.7
PM
192
48.2
AM
22.6
17.3
PM
733
100
Left
WB old TH 12
Through
Right
Wayzata Boulevard
Right
Left
Montessori Right Turns onto WB old TH 12
Queue Lengths - pm
WB TH 12
WB TH 12
EB TH 12
EB TH 12
MN Hwy 22 at Co Rd 90 - alternatives
Signal with 3-in, 1 out geometry
Single lane roundabout
Multi-lane roundabout
Hwy 22 at Co Rd 90 - Project Issues
• Evaluate roundabout versus traffic signals
• Evaluate single lane versus multi-lane roundabout
• Evaluate cost effectiveness of design features
• Document the overall benefits
• VISSIM results recommended the multi-lane design
 Will operate as a 1.5 roundabout with added through
lane as passing opportunity
 Roundabout geometry will work with future divided
roadway alignments
Lessons Learned
Lessons Learned - VISSIM
• Use “special" links on approaches and exits to network
 Constant locations for traffic inputs, routing decisions, speed
limits and beginning of travel time traps, creating alternatives
that are consistent is much easier
• Consider using only a physical headway rather than time gap for
roundabout entry priority rules (matches driver decision making
more realistically)
•
Add a further speed reduction (below curve speed) at Yield line
• Run links into the roundabout as 4 through routes, make all turns
with connectors, rather than having a circular roadway
• Create short links at Yield lines with lane closures
• Use separate right turn priority rules under certain conditions
Lessons Learned - VISSIM
• ICE requirements require “total” travel time
evaluations not just VISSIM node evaluations
• Don’t try using general speed zones for the
roundabout environment, use curve speed areas
• The batch run feature works well
• Consider the connector decision distance as travel
time (rather than feet) and reduce accordingly based
on the lower speed environment of a roundabout,
particularly if closely spaced multiple roundabouts
• Also consider the emergency stop distance (16.4 ft) is
way too short for lane drops and some decision
points
Lessons Learned - VISSIM
• Vehicle tracking is useful tool (no need to keep
checking in Autoturn)
• Easy to:
 Measure queues
 Assess impacts of nearby intersections
 Assess pedestrian impacts
 Demonstrate and measure the effects of geometric
changes
 Visualize results of design decisions
• VISSIM is an effective presentation tool for elected
officials
Checking vehicle tracking in VISSIM
Lessons Learned – Roundabout Selection
and Design
• Planning – Understand roadway system issues, mobility versus
access
 Roundabouts tend to “equalize” the network and favor access
over mobility
• A roundabout is both an intersection and a traffic control
device, the issue of “warrants” is complex
• Consider all hours and volume levels of operation, not just the
peaks
• Understand the range of variability of the forecasts
• Consider all modes and vehicle types that will use the
roundabout
• Roundabout geometry does affect capacity and efficiency, but
in ways not apparent in RODEL
 Use wide splitter islands
• Better gap selection
• Better deflection
Roundabout splitter width test
5 % more capacity
5 to 7 seconds reduction in travel times
Reduced truck off-tracking
However…
Roundabouts have a “cult”
following in some places
Don’t be pressured
Do the math
Politician, Planner or
Landscape Architect
Traffic
engineer
“Standard” Conflict Diagrams
Roundabout
Intersection
X X X X
X X X
X X
X
X
X
XX XX
“True” roundabout conflict points
X
X
X
X
The End
Questions?