MULTI-LANE

ROUNDABOUT

DESIGN

1

HOW DOES A MULTI-LANE

ROUNDABOUT DESIGN DIFFER

FROM A SINGLE LANER?

2

OLD FHWA Recommendations

Offset Left Now Preferred

by Many Organizations

Design Steps

1ST – place 150’

diameter circle at

center of existing

intersection. All

work being done

at this point is with

paint lines – curb

lines are just

offsets from the

paint lines

Design Steps

2nd – copy 150’

diameter circle

parallel around

18’ or so twice –

once for the

travel lane and

another time for

the truck apron

NOTE: later you

will need to

check with

AutoTurn,

AutoTrack or a

similar program

Design Steps

3rd – use a 300’

to 800’ fillet to

tie the center

line to the exit

side of the truck

apron and the

left edge line to

the outside of

the roundabout

– use the same

radius to let

CAD worry

about the taper..

Design Steps

4th – copy the

new center line

over 12’ for your

new right edge

line

Design Steps

5th – use a 90’ to

110’ fillet to tie in

the approach.

Use the same

radius on both

sides – let CAD

take care of the

taper…

RESULT

One leg is done

– you now have

an approach

with geometry

that requires

vehicles to slow

down before the

yield line. This

technique has 2

points of speed

reduction – you

have staged

and staggered

the speed

reduction

RADIAL

This layout

technique has

only 1 point of

speed reduction

and it is at the

pedestrian and

circulating

vehicle conflict

area. Also, the

driver does

have a clear

view into the

roundabout

DOES

THIS

WORK?

Can you utilize

single lane design

techniques on 2

lane roundabouts?

DOES

THIS

WORK?

NO

There is one critical

design error that

needs to be

addressed…

What is wrong?

ENTRY

PATH

OVERLAP

Think about the

driver….

They get to the yield

line – look left –

then look straight

ahead – they forget

about the 100’

radius that they

have just been

following

Multi-Lane Roundabout Issues

Entry path overlap

Design vehicle tracking

On approach

Within circulatory roadway

Signing & Striping critical to achieve

desired lane use…

Entry Path Overlap Example

Which lane do I want to enter???

Which lane would you likely enter???

Offset Left Design Demonstrated

and Entry Path Overlap Eliminated

per NCHRP 672

CAD Steps for 2 Laners

CAD Steps for 2 Laners – Guestimating?

CAD Steps for 2 Laners – 1 car length

CAD Steps for 2 Laners – Tangents Done

CAD Steps for 2 Laners – 6’ Offset Method

CAD Steps for 2 Laners – Now 140’ +/- Fillets

CAD Steps for 2 Laners – Almost Identical

2 lane Approach Layout

we are now using 14 or 15’ wide lanes and a 4 or 6’ gore

2 lane Approach Layout

Entry Path Overlap Check

Improved Driver View From Yield Line

Desired View From Yield Line

What Can You Do If Already Built?

Entry Path Overlap “Fixed” With Striping

Entry Path Overlap FIXED! http://teachamerica.com/RAB11/RAB1109Vorisek/player.html

What about a WB-67 Design Vehicle?

MUTCD Path Overlap

MUTCD Path Overlap –

What Happens to Red Car?

Entry/Circulatory Roadway Tracking Truck Gore Striping was Implemented

Left Approach Lane Tracking With Truck Gore Striping

DOTD is recommending Case 2 Designs

Anyone know how much over-tracking is OK

Case 1 - Undesired Circulatory Track Every roundabout design should be checked for truck tracking

Kingston Roundabout Striping

If you sign it like a single lane it will function as a single lane

“Typical” 4 way intersection

Slight Circular Adjustment

Malta - Possible Moves

Rt 67 at US 9 in Malta, NY

Trucks Turn Left from Right Lane – Why???

Rt 67 at US 9 in Malta, NY

Cars Turn Left from Right Lane – Why???

Latham Traffic Circle Retrofit - Before

Latham Traffic Circle Retrofit - After

Latham Multi Lane Approach – Before

Alignment, Signing & Striping

Latham Multi Lane Approach – After

Alignment, Signing & Striping

Latham Multi Lane Approach Signing

NYSDOT Multi Lane Roundabout Signing

NEW NYSDOT Multi Lane Signs

NEW NYSDOT Multi Lane Arrow Placement

NEW NYSDOT Multi Lane Arrow Placement

NYSDOT 2 Lane Roundabout –

arrows still need to be moved

RT. 9 @ RT. 67 ROUNDABOUT

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58

RT. 9 @ RT. 67 CRASH DIAGRAM

PROBLEMS: 1) Lefts from right lane

2) Outer lane not

yielding to inner

circulating lane

3) Higher than desired

approach speeds

4) Tight ROW led to

small radial design

with large entry radii

59

RT. 9 @ RT. 67 CRASH RATE –

Some changes worked

better than others

60

YIELD “TO BOTH LANES” Signing

Here is what we hope the new sign resolves

A CONCERN WITH RBT ANALYSIS • MOST PROGRAMS ASSUME AN AMOUNT OF

“DOUBLING UP” OR “RUNNING SIDE BY SIDE”

― but what if 1 lane flares to 2 without much

circulating flow in front of it

― to better balance delay between legs

• WHEN TO CONSIDER A SIGNALIZED ROUNDABOUT?

― when 1 or more dominant legs have little delay

but cause significant delay to minor approach

• HOW DOES IT WORK?

― the signal stops the dominant leg – allowing

minor leg to enter the roundabout

• WHAT DOES IT LOOK LIKE?

― the following image is from Clearwater, FL

SINGLE LANE FROM NORTH WITH HIGH VOLUME CAUSES DELAY ELSEWHERE

― the signal stops the dominant leg – allowing

minor leg to enter the roundabout

• WHAT DOES IT LOOK LIKE?

― the following image is from Clearwater, FL

ADDITIONAL LANE FROM NORTH IMPROVES DELAY FOR OTHER LEGS???

― the signal stops the dominant leg – allowing

minor leg to enter the roundabout

• WHAT DOES IT LOOK LIKE?

― the following image is from Clearwater, FL

ADDITIONAL LANE FROM NORTH IMPROVES DELAY FOR OTHER LEGS???

― the signal stops the dominant leg – allowing

minor leg to enter the roundabout

• WHAT DOES IT LOOK LIKE?

― the following image is from Clearwater, FL

METER NEEDED TO BE ADDED

Thank you to Everyone

Here Today and

To All that Contributed

to this Conference