Alexander Road Bridge Over Amtrak’s Northeast Corridor (NEC)
West Windsor Township, Mercer County
Old Bear Brook Road
Existing
Proposed
Alexander Road
Amtrak’s Northeast Corridor
North Post Road
Wallace Road
Emil Street
Woodmeadow Lane
Alexander Road
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Alexander Road Bridge Over Amtrak’s Northeast Corridor (NEC)
West Windsor Township, Mercer County
Alexander Road
Traveling toward Roundabout
Alexander Road
View of Mark’s Trackside Auto Center
West Approach - View of Bridge
Alexander Road - East Approach
North Post Road - West Approach
Alexander Road - East Approach
Frontage Road - View From West
Frontage Road - View From East
Frontage Road - View of Retaining Wall
Aerial View of Roundabout
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WHAT IS A ROUNDABOUT?
A modern roundabout is an unsignalized circular
intersection engineered to maximize safety and minimize
traffic delay. Over the last few decades, thousands of
roundabouts have been installed in Europe, Australia
and other parts of the world. Recently, they have gained
support in the United States with states such as
West Coast, Mid-West and East Coast, and more
recently, New Jersey, getting experience with their use
and design. Drivers in those states also are becoming
comfortable with their use. In the cities and towns
where roundabouts have been built, and even where the
public has been hesitant about accepting them initially,
roundabouts ultimately have been accepted
enthusiastically because of the increased safety they
provide, along with traffic calming, and aesthetic
benefits. Depicted below is the roundabout replacing the
Alexander Road - North Post Road Intersection.
15’ Radius Truck Apron
IN THE UNITED STATES, WHERE ARE ROUNDABOUTS?
Interest in roundabouts has been growing in the United
States. Several hundred are now in place. Roundabouts
have proven to be particularly effective at intersections
with large numbers of left turns. They are also effective
at places with moderate to high entering traffic volumes,
and at the ends of freeway on and off ramps. In addition,
they offer special advantages at the intersections with
more than four legs.
Oregon
Colorado
Michigan
25’ Radius Center Island
Splitter
Island
Maryland
Circulatory Roadway
Sidewalk
Colorado
Kansas
Florida
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Recently Constructed Roundabouts in New Jersey
Princeton University Campus Roundabout - Princeton
Township, Mercer County
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Rutherford Square Station
Rutherford, NJ
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NJDOT Conceptual Design Projects with Modern
Roundabout Configuration Under Construction
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Crossroads Re-Development Area, intersection of Routes 73, 90, US
130, and Haddonfield Road, Pennsauken Township, Camden County
Lambertville/Gateway - West Amwell Township, Hunterdon County
Route 41 & Route 47 - Deptford/Washington Township, Gloucester
County
Route 322 & C.R. 551 - Woolwich Township, Gloucester County
Route 130 Corridor Study - Pennsgrove and Carneys Point, Salem
County
Route 322 & Rowan Blvd. - Glassboro Township, Gloucester County
East Main St. & South Main St. - Bound Brook Township, Somerset
County
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Other Roundabouts in the US
Rt-219 Scaggsville, Maryland
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US-6 Avon, Colorado
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Comparison between Modern Roundabouts and Traffic Circles
ROUNDABOUTS ARE NOT TRAFFIC CIRCLES
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Roundabout
Employs traffic calming characteristics.
Entering traffic yields to circulating
traffic, which always keeps moving.
Very efficient with heavy traffic.
No weaving distance is needed, so
roundabouts are small and fit in compact
spaces.
Deflection controls speed without
enforcement, thereby reducing accidents.
Deflection forms gaps in traffic so other
vehicles can enter.
Flare promotes narrow streets between
roundabout, saving cost and neighborhood
impacts.
Roundabouts are designed to require a
speed reduction, often times to the 15-20
mph range.
Diameter is calculated based on traffic
volumes and movements and are much
smaller.
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Traffic Circle
Circulating traffic can not clear when
entering traffic fills circle
Heavy traffic causes gridlock.
Circles must be large to provide long
weaving distances.
Serious accidents can result on high speed
streets.
Fast entries impede gap acceptance and
defeat the yielding process.
Higher capacity requires wide streets
between circles, wasting money and land.
Traffic Circles are designed to maintain
the prevailing roadway speed, often times
35 mph and up.
Diameter is arbitrarily determined by the
space available and is often very large,
allowing higher speeds and unsafe
conditions.
Traffic circles are not pedestrian friendly
within a community setting.
New Jersey Department of Transportation has been maintaining a program for the past
several years to eliminate obsolete traffic circles in New Jersey.
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Myths and Facts about Roundabouts
Myth
Roundabouts cause longer commutes.
Roundabouts are difficult to maneuver.
Fact
Roundabouts keep traffic moving. The major delay on a person’s morning or evening
commute is usually the time spent sitting at traffic signals. Eliminating the need to stop
and wait reduces delay.
Using a roundabout is the much the same as making a "right turn on red." At a traffic
signal, a right-turning driver stops at the stop bar, looks for conflicting traffic coming
from the left, chooses an acceptable gap in the traffic flow, and then turns right onto the
cross street. At a modern roundabout, the oncoming driver approaches the yield line,
looks for conflicting traffic coming from the left, chooses an acceptable gap in the traffic
flow, and then enters the roundabout with a right turn at the yield sign.Once inside the
roundabout, a driver continues circling counter-clockwise until reaching the desired exit.
Exit maneuvers are also right turns.
Roundabouts are not safe for pedestrians.
Roundabouts are very pedestrian friendly. The splitter islands provide a space for
pedestrians in the middle of each crossing. Therefore, pedestrians only need to cross one
direction of traffic at a time. The pedestrian crosswalks are set at least one full car length
back from the yield line. That way, pedestrians do not have to cross in front of drivers
that are looking for their gap in traffic. Experience has shown that the stopped vehicle
one car length back from the yield line is more aware of pedestrians.
Roundabouts cause more accidents
than the stops signs or traffic signals
that they replace.
According to the Insurance Institute for Highway Safety, modern roundabouts reduce
motor vehicle crashes. Their July 2001 Status Report noted "most serious kinds of
crashes at conventional intersections are virtually eliminated by roundabouts…Crashes
that do occur tend to be minor because traffic speeds are slower." The study reviewed 24
intersections around the U.S. that have been converted from stop signs or traffic signals
to modern roundabouts. At those intersections, all crashes were reduced by 39%. Serious
crashes were reduced by 76%. At the time of the study, there had been no
fatalities at any of the new roundabouts. So, the study estimates that fatal or
capacitating injuries will be reduced by 90% at those intersections.
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SAFETY AND OPERATIONAL PERFORMANCE
How can such impressive accident reductions be
explained? One reason is that there is a reduction in the
number of conflict points within the facility. As the figure
below shows, a standard intersection has 32 potential
vehicle-to-vehicle conflicts versus 8 for a roundabout. In
addition, modern roundabouts are designed such that
traffic enters at nearly right angles to the circulating
traffic. The merging lanes that characterized traffic
circles (and led to confusion over who has the right-ofway) have been eliminated. Third, roundabouts are
relatively small, particularly when compared with typical
traffic circles. So, traffic speeds are slower, there are
more opportunities to enter circulating traffic, and fewer
accidents result.
NAVIGATING A ROUNDABOUT
Motor Vehicles
Approaching and Entering the Roundabout
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When approaching the roundabout, follow the lane
designation signs, slow down and yield to pedestrians in
the crosswalk.Look to the left.
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Traffic in the roundabout has the right-of-way.
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Approach the yield line and enter the roundabout when
there is an adequate gap in the circulating traffic flow.If
another car is waiting at the yield line ahead of you, do
not stop in the crosswalk.
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Keep the crosswalk clear for pedestrians.Bicyclists are
permitted to ride within the roundabout.
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Please share the road and do not pass a bicycle in the
roundabout.
Conflict Point Illustration
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Navigating a Roundabout
Motor Vehicles
Exiting the Roundabout
• Once you have entered the roundabout,
proceed counter-clockwise to your exit.
You now have the right-of-way.
• As you approach your exit, turn on your
right turn signal.
• Exit the roundabout, yielding to pedestrians
in the crosswalk.
Trucks
• Drive on the circulatory roadway, except
large trucks and trailers may use the truck
apron provided to negotiate the tight turning
radius.
• Drive (usually with just the rear wheels) on
the raised pavement of the truck apron to
navigate more easily.
• Cars should not use the truck apron.
• Emergency vehicles such as large fire
engines can easily navigate the roundabout
by riding over 15’ inner truck apron.
Pedestrians
• Stay on the designated walkways at all
times.
• Cross only at the designated crosswalks.
• Never cross to the central island.
• Watch for cars; you have the right-of-way,
but your best protection is your own
attention.
• Cross the crosswalk one lane at a time,
using the splitter island as a refuge area
before crossing the next lane.
Bicyclists
• You are strongly encouraged not to ride
within the roundabout itself. Studies have
determined that the safest way to proceed
through a roundabout intersection is to walk
your bicycle.
• If you are comfortable riding in traffic, take
the lane and circulate like you are a vehicle,
making sure you yield to traffic in the circle
when entering.
• Ride at the speed of the circular roadway to
discourage cars from passing you.
• When you exit the roundabout, use your
right hand signal.
• If you are unsure about using the
roundabout, dismount and walk your bike
as a pedestrian at the designated crosswalks.
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Crosswalk Treatments
Brick
Painted Crosswalk
Street Print
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Truck Apron Treatments
Asphalt
Cobble Stone
Brick Pavers
Structured Asphalt
Stamped Concrete
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Center Island Treatments
Grass Island
Landscaped Island
Asphalt Island
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Formliners (Retaining Wall Treatments)
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Recommended Shrubs
ABELIA X GRANDIFLORA Glossy Abelia
FORSYTHIA X INTERMEDIA
‘SPECTABILIS’ Showy Border Forsythia
CORNUS SERICEA
‘FLAVIRAMEA’ Yellowtwig
Dogwood
ILEX VERTICILLATA
Hybrid Winterberry
PRUNUS LAUROCERASUS
‘OTTO LUYKEN’ Otto Luyken
Hybrid Cherry Laurel
CORNUS SERICEA
‘SIBIRICA’ Tatarian
Dogwood
ITEA VIRGINICA ‘HENRY’S GARNET’
Henry’s Garnet Virginia Sweetspire
VIRURNUM TRILOBUM ‘COMPACTUM’
American Cranberrybush Viburnum
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Recommended Trees
ACER RUBRUM Red Maple
BETULA NIGRA ‘HERITAGE’
Heritage River Birch
MAGNOLIA VIRGINIANA
Sweetbay Magnolia
CRATAEGUS PHAENOPYRUM
Washington Hawthorn
CRYPTOMERIA ‘YOSHINO’
Japanese Cryptomeria
CORNUS MAS
Corneliancherry Dogwood
NYSSA SYLVATICA
Black Gum
PINUS STROBUS ‘FASTIGIATA’
Columnar White Pine
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