Roundabouts: Why is Mn/DOT Building Them?

Traffic TopicsAugust 5, 2010

Ken E. JohnsonMn/DOT Office of Traffic, Safety, and Technology

Member of Mn/DOT Roundabout Steering Committeeken.johnson@state.mn.us

651-234-7386

Ken’s RA Biography

• Experienced RAs in Ireland in 1999 & 2001– The only intersection I didn’t need to think about

• Roundabouts: It’s Time for Minnesota– Capstone project for Masters degree– Coauthored with John Gorder and Brian Malm

• Member of Mn/DOT’s Roundabout Steering Committee and Roundabout Review Team

Introduction to Roundabouts• Why consider roundabouts?• What is a roundabout – what is a traffic circle?• What’s so great about them anyway?

– Advantages and Goals• Location considerations• What’s happening at Mn/DOT?

– How do we decide?– Changes to traffic control devices

Mn/DOT Strategic Directions• Safety• Mobility• Innovation• Leadership• Transparency

The appropriate application of Roundabouts is in line with 3 of the Strategic Directions of the Department

Roundabouts are …• Not social engineering

• Merely one type of intersection control made of concrete, asphalt, gravel, dirt, etc.

• One of the tools that traffic engineers use to control crossing traffic.

• Not the Europeanization of America• Not the solution for world peace

Intersection Controls• Why – because that’s where vehicles cross paths

which leads to delay and the possibility of crashes• Types

– Yield controlled– TWSC (Two way stop controlled)– AWSC (All way stop controlled)– Signalization– Roundabouts– Continuous flow intersections and other non-typical types

TWSC Intersections• Mn/DOT’s good old default

– Mobility is our major goal

• But what if there are problems…– Crashes– Side street traffic gets heavy enough that excessive delay occurs to the

minor road traffic

• AWSC – usually very safe, but bad for delay• Signals – can help with delay, but safety can be issue• Interchanges - $$$$$

• Roundabout – in appropriate application, very safe and has less delay than other intersection types

Introduction to Roundabouts

The image that many American’s have…

Unfortunate misconception

Video courtesy of Mark Johnson, MTJ Engineering

Not Traffic Circles, Rotaries, etc.Modern roundabouts vs. traffic circles:• Yield on entry – first rule (UK 1966)• Counter-clockwise circulation• Lower speeds necessary - deflection

– Splitter islands– Central island

• Pedestrian movements restricted to crossing legs• No parking

First RB in USA – Summerlin, NV early ‘90s

Roundabout Features

Roundabouts: An Informational Guide – FHWA, Exhibit 1-2

Introduction to Roundabouts

This is an example of a modern roundabout…

Types of Roundabouts and Typical Volumes

Type Typical Diameter

Typical Entering Volumes

Mini-roundabout

45-90’ 15,000 ADT

Single lane 90-180’ 25,000 ADT (34,000 in FL)

Multi-lane 150-300’

45,000 – 70,000 ADTAssuming 4 perpendicular legs with balanced flowsIn general, can handle similar volumes as signals that are not failing

Rough Entering Volumes

Intersection 2005 Entering Volumes

Co Rd B2 and Dale 12,000 ADT

Larpenteur and Dale 27,150 ADT

Co Rd B and Lexington

24,000 ADT

TH 51 and Larpenteur Ave

53,000 ADT

That much traffic?Signal – 4,400 vph

Loveland, CORoundabout - 4,000 vph

Avon, CO

Video courtesy of Bill Hange, City of Loveland and Mark T. Johnson, MTJ Engineering

Video courtesy of Leif Ourston,

Ourston Roundabout Engineering

Advantages – Reduced Delay• Delay is the difference between

– Travel time with no intersection control– Travel time with intersection control

• Includes slow down, stop, and speed up time

• Always better than AWSC• Usually better than TWSC if minor road

volumes are close to major road volumes• 50/50, 60/40, 70/30

• Usually better than signal

Delay Reduction - Signalized

“Average delay per vehicle at the MUTCD peak hour signal warrant thresholds” for various

volumesRoundabouts: An Informational Guide – FHWA,

Exhibit 3-7

Advantages – Increased Safety

Reduced conflict points (8 vs. 32)Roundabouts: An Informational Guide – FHWA,

Exhibit 2-3

Advantages

• Increased safety (continued)– Shallow angle of conflict– Slower speeds

• Better reaction time• Reduced severity of crashes

– Energy = ½ x mass x speed x speed

– Simplified decision making• Right turn at residential T-intersection

Simple decision – Wait for opening(right turn at residential T-intersection)

Safety – National Studies

Mean Total Crash Rate

(Crashes/ MVE)

Mean Injury Crash Rate

(Crashes/ MVE)

Before Period 1.53 0.97After Conversion 0.48 0.11% Reduction 68% 89%

Source – Maryland State Highway Administration, 2001

Maryland – 8 single-lane rural roundabouts studied

Each replaced stop signs or intersection control beacons

Safety – National StudiesInsurance Institute for Highway Safety - 2000

• Crash Reductions Following Installation of Roundabouts in the United States

• 24 intersections in 8 states converted to roundabouts

• 39% Reduction in All Crashes• 76% Reduction in Injury Crashes

Safety – National StudiesRoundabout Characteristics Before Condition # of Sites

Total PDO InjurySingle Lane,Urban Stop Controlled 12 69% 67% 80%Single Lane,Rural Stop Controlled 9 65% 63% 68%Multi Lane,Urban Stop Controlled 7 8% 0% 73%Urban Signalized 5 37% 31% 75%All Sites 33 47% 41% 72%

Percent Reduction in Crashes

Source – Insurance Institute for Highway Safety and NYSDOT, 2003

NCHRP Report 572-Roundabouts in the US (2007)

-76%-35%

-87%-72%-71%-32%-81%-29%

-67% TOO FE W

S IMIL A R S IMIL A R

-60%SIMILAR

Safety – Increased Ped Safety

Source – Roundabouts: An Informational Guide (FHWA)

Safety – Increased Ped Safety• Shorter crossing distance• Pedestrian only looks one direction• Drivers at signals watch the light• Drivers at typical intersections tend to look left and

turn right• Pedestrian crossing separated from intersection –

allows driver to pay more attention to pedestrian

Safety –Pedestrian Safety• Disadvantage is that vehicles aren’t necessarily

stopping• Reduced speeds help

• Possible issues with visually-impaired pedestrians

Safety – Pedestrians

20 mph 30 mph 40 mph 50 mph0%

10%20%30%40%50%60%70%80%90%

100%

5%

40%

80%

100%

Chance of Pedestrian Death If Hit By a Motor Vehicle

Literature Review on Vehicle Travel Speeds and Pedestrian Injuries – Final Report DOT HS 809 021, October 1999

Safety – Pedestrians

Type of Roundabout Injury Rate/ 1 million pedsMini Roundabouts 0.31Small Roundabouts 0.33Conventional (2 lanes) 0.45Large (2+ lanes) 0.72Traffic Signals 0.67

Source – TRRL Lab Report 1120, 1984

United Kingdom Experience

Safety – Pedestrians• Pedestrian Study in Melbourne,

Victoria (Australia)– Source: Andrew O’Brien & Associates Pty

Limited– Roughly the same size/population as 7

County Twin Cities Metro area– ~4000 roundabouts– 1996-2000

– 57 total pedestrian crashes from 1371 overall crashes

– 0 fatalities– 32% required hospitalization

Safety – Pedestrians

Victoria, Australia anecdotal experience• Source: Andrew O’Brien & Associates Pty

Limited• Black Spot Program – fix intersections with

serious crash rates – to be eligible, there must be 3 injury/fatal crashes in a 3 year timeframe

• Over 5000 roundabouts in Victoria• Roughly the same size/population as

MN• All pedestrian black spot intersections in

Victoria are signals

Advantages

• Reduced environmental impacts– Less fuel consumption– Vehicle emissions reduced

• 33% less hydrocarbons• 36% less CO• 21% less nitric oxides

– More pleasant to live next to…

Case Study – TH 13 and Scott County Rd 2

• Rural TWSC Intersection of High-Speed Roads• 2000-2004 (5 year period)• 26 injury, 9 property damage, 2 fatal

crashes• 50 injuries and 2 fatalities

• Roundabout opened to traffic in Sept 2005• Sept 2005 - August 2010• 5 reported crashes• 3 injuries and no fatalities

Case Study – TH 13 and Scott County Rd 2

Case Study – Golden, CO• South Golden Road in Golden, Colorado

– Before condition– ¾ mile segment of 4-lane expressway with TWLTL– Almost indiscriminate private business driveways– Two signals – Ulysses and Johnson– Proposed additional signal in corridor– Corridor serve several residential neighborhoods, many

businesses including fast food restaurants and gas stations, and other retail outlets

– High and middle schools located ¼ mile from corridor

Source: Alex Ariniello, LSC Transportation Consultants

South Golden Road before improvements

Case Study – Golden, CO

4 roundabouts constructed in 1998 – 99

Case Study – Golden, CO

South Golden Road ExperienceRoundabouts in Series (2004

information)• Travel Time through Corridor Reduced

• 78 sec (expected to go to 103 sec) to 68 sec

• Intersection Delay Reduced• Access to Businesses Delay Reduced

• Before – average 28 seconds, maximum 118 seconds

• After – average 13 seconds, maximum 40 seconds

• Right turn/U-turn Safer and Quicker than Left Turn In

• 85th percentile Speed Reduced from 47 mph to 33 mph

3 years prior

(96-98)

7 years after

(00-06)

Accident Rate

Reduction

Total Accidents 360 150 - 85%

Injuries 31 3 - 96%

Average Daily Traffic

11,500 15,500 + 35%

Accident Statistics Provided by Public Works Director

South Golden Road ExperienceRoundabouts in Series

Good for Businesses

In 2004, sales tax revenues had increased 60% since roundabouts constructed – only portion of city that had seen increase each year, even during an economic slowdown. Plus, over 75,000 sq ft additional retail/office space added.

• Entering volumes less than 8,000 vph• Roughly same functional classification

• Arterial/arterial, collector/arterial, collector/collector

• Entry volumes balanced = higher capacity• The upper capacity limits of a roundabout

will be higher with balanced flows.• However, this guideline depends on overall

volume.• Heavy mainline travel (ie 90/10) – signal

may outperform a roundabout, but needs to be analyzed on a case by case basis.

• All levels of pedestrian volumes

Where are Roundabouts Appropriate?

Locations Not Recommended for a

Roundabout • Corridors with a well operating coordinated

signal system• Where Satisfactory geometric designs can’t

be provided (doesn’t have to be ideal)– Deflection– Inscribed circle diameter– Roadway width– Approach grades

• Locations with unusual geometry or number of legs

• Rural intersections with high crashes or high delay

• Intersections with high amounts of left turns on one or more legs

• Interchange locations with right of way, bridge width, or bridge crest restrictions

• Near schools or playgrounds• Through small towns or commercial

corridors (combined with access management)

Where Roundabouts May “Shine”

• Concern that MN drivers will find them confusing

• Nationwide experience• Similar amount of crashes as signals• Still ~75% reduction in injury crashes• Most typical crashes are caused by not

following the signs• Failure to yield to both lanes at entry• Exit conflict

• Some education efforts underway• Best advice – follow the signs and pavement

markings

What About Multi-lane Roundabouts?

What About Multilane Roundabouts?

What’s Mn/DOT Doing?• Developed Roundabout Chapter in Road Design

Manual• Intersection Control Evaluation

– Any intersection that requires more than a TWSC will require ICE to choose correct intersection application• All way stop• Signal• Roundabout• Other

What’s Mn/DOT Doing?• Roundabout projects will have extra reviews

– Same level of reviews as freeways– Roundabout Review Team

• Updated State Aid Roundabout Design Checklist– Guidance to cities and counties

• Updating Minnesota Manual of Traffic Control Devices– Based on Federal MUTCD (2009)– Many changes for roundabouts

What’s Mn/DOT Doing?• Education efforts

– Roundabout webpage – google mndot roundabouts– “Roundabout on a stick” – handed out last year at State

Fair– Minnesota State Map– Per project– Washington County Roundabout “U”

- google roundabout u

Roundabouts in MN• State Highway System (existing)

– I-35 and Steele County Road 12 near Medford Outlet Mall (2 at ramp intersections)

– TH 13 and Scott County Road 2 near New Prague– Elm Creek Roundabout in Maple Grove (connected to

future TH 610)– TH 7 with TH 25 and Carver County Road 10– TH 61 and Jamaica Avenue in Cottage Grove (2 at ramp

intersections)– TH 3 and 190th Street in Farmington/Empire Township

Roundabouts in MN• State Highway System (existing)

– TH 3 and 80th Street East in Inver Grove Heights– TH 52 and Wentworth Avenue in West St. Paul and

South St. Paul (2 at ramp intersections)– TH 284 and 15th Street in Waconia– TH 19 and Chalupsky Ave in New Prague– TH 19 and Alton Ave in New Prague

• All roads – State Aid Office List (self-reporting)– 80 constructed and in operation as of Feb 2010– http://www.dot.state.mn.us/stateaid/ - Roundabout List

Roundabouts in MN• State Highway System (under construction)

– TH 5 and Jamaca Ave/Stillwater Blvd in Lake Elmo– TH 61 and Washington County Road 2 in Forest Lake

Is this the future?

• Victoria, Australia– Pop ~5 million– Area ~238,000 km2

– Density ~22 / km2

• Melbourne, Victoria– Pop ~3.7 million– Area ~7700 km2

– Density ~480 /km2

• Minnesota, US– Pop ~5 million– Area ~225,000 km2

– Density ~24 / km2

• 7 Co Metro Area, MN– Pop ~3.1 million– Area ~ 7700 km2

– Density ~400 /km2

Is this the future?• Victoria, Australia

– 1973 – 3 roundabouts in Victoria– 2006 ~5000 roundabouts in Victoria– In this timeframe, removed 3

• Melbourne, Victoria– 2006 ~4000 roundabouts in Melbourne– Largest RB in Melbourne

• Andrew O’Brien, Intersection Designer in Victoria• ~50,000 ADT on one road• ~20,000 ADT on crossing road

Questions??

Near Medford, MN - Photo courtesy of Mn/DOT