VISSIM and Mn/DOT’s INTERSECTION CONTROL

EVALUATION (ICE) VISSIM USER’S GROUP MEETING

MAY 15-16, 2008Philadelphia

Dennis Eyler, P.E., P.T.O.E.

Vice President

SRF Consulting Group, Inc.

deyler@srfconsulting.com

Leif Garness, E.I.T.

Traffic Engineer

SRF Consulting Group, Inc.

lgarness@srfconsulting.com

Presentation Overview

• What is ICE?

• Issues with ICE

• Two examples of ICE for roundabout projectsOld US 12 at Wayzata BoulevardMn Hwy 22 and Blue Earth County 90

• Lessons learnedUsing VISSIM for roundaboutsRoundabout Design

ICE OVERVIEW

• 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 – Definition and Goals

ICE Flow Diagram

Intersection Alternatives

• Standard intersections Mn/DOT minimum for

signals• 3 lanes (L-T-R) in, 1

lane out

• Roundabouts

• One way pairs

• Offset “T’s”

• Quadrant roadways

• Michigan U (left) -turns Continuous flow or lefts in advance

• Jug handle

• Through-about

• Super street

• Reduced conflict

• Double cross-over

At-grade Intersection Alternatives

Indirect or “Michigan”

U (left) turns

No left turns

Quadrant intersection

No left turns

Patented by F. Mier

CFI

Continuous flow

intersection Jug handle Through about

• 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 – Planning Level Evaluation

Traffic Volume Input Sheet

SRF Intersection Evaluation Tool

Intersection Alternatives - Worksheet

Right turn bypass?

Number of lanes

Results are V/C ratios

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?

• 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?

Warrant Status

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 roundaboutShow that there is no safety issueShow that there are no capacity or efficiency

issues during the interim until warrants are met

• 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

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

Roundabouts – waiting to enter

Signals – waiting for green

All-way stops – waiting for turn

Side street stops – waiting for gap

5. Congestion delay to other traffic going in the same direction (e.g. queue discharge or following a truck)

Controls and Travel Time

Traffic control impacts total travel time

(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

Added Travel Time(1) Due to Major Speed Changes

• CARS

• Stop sign 35 to 0 to 35 = 14.2 secs 65 to 0 to 65 = 24.4 secs

• Roundabout - 15 mph (2) 35 to 15 to 35 = 9.1 secs 65 to 15 to 65 = 18.6 secs

• TRUCKS

• Stop sign 35 to 0 to 35 = 19.7 secs 65 to 0 to 65 = 45.0 secs

• Roundabout - 15 mph (2) 35 to 15 to 35 = 20.7 secs 65 to 15 to 65 = 46.8 secs

Travel time “trap”

free flow

Collect total travel time for all vehicles from approaching at free flow speed to returning to free flow speed

Project Examples

Project Examples

• 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

North

Old US 12 at Wayzata Boulevard

New US 12 freeway

Construct roundabout

Close access

Add frontage roads

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

Left AM 2.3 2.2

PM 5.5 0.1

WB old TH 12 Through AM 0.4 1.0

PM 0.9 3.6

Right AM 1.4 2.7

PM 1.4 4.2

Wayzata Boulevard Right AM 7.2 0.2

PM 19.7 10.8

Left AM 32.8 1.7

PM 15.3 21.1

Montessori Right Turns onto WB old TH 12 AM 14.8 15.2

PM 55.1 27.2

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

Left AM 3.3 2.4

PM 13.6 1.7

WB old TH 12 Through AM 0.5 1.3

PM 1.4 4.0

Right AM 1.4 1.0

PM 1.6 2.9

Wayzata Boulevard Right AM 19.4 1.9

PM 229 36.2

Left AM 75.6 6.7

PM 192 48.2

Montessori Right Turns onto WB old TH 12 AM 22.6 17.3

PM 733 100

Old US 12 – Results – 2028 volumes

Queue Lengths - pm

WB TH 12 EB TH 12

WB TH 12 EB TH 12

MN Hwy 22 at Co Rd 90 - alternatives

Signal with 3-in, 1 out geometry

Multi-lane roundabout

Single 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

• 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

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 capacity5 to 7 seconds reduction in travel timesReduced 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

X X X X

XXX

X

XXX

XX X X X

Roundabout Intersection

“True” roundabout conflict points

XX

X X

The End

Questions?