Transcript Roundabouts: The Ins & Outs

Roundabouts:
Myth Busters
Presented by:
Sonja Piper, PE
Common Roundabout Myths


Drivers can’t learn or won’t
accept
−
Elderly drivers
−
Near schools

Difficult to maintain and
plow snow

Only a traffic calming tool
Dangerous
−
Vehicle traffic
−
Pedestrians and bicyclists
−
Icy conditions

Expensive

Large vehicles can’t
navigate

Emergency vehicles may
be impeded
−
Lower capacity than
traffic signals
−
Longer delays
−
Roundabouts build out
East are being removed

Shouldn’t be used on highspeed roads

Roundabouts are bad for
business
Roundabout Myth Busting:
Drivers Can’t Learn or Won’t Accept
Attitude
Before
Construction
23%
After
Construction
0%
Negative
45%
0%
Neutral
18%
27%
Positive
14%
41%
Very Positive
0%
32%
Very Negative
Roundabout Myth Busting:
Drivers Won’t Learn
 City of Cottage Grove Public Safety/Public
Works comments:
− Police Chief Wilson
 “…safest intersection in Cottage Grove”
 “our guys love it”
− Public Works Director Burshten
 “it really works well”
Roundabout Myth Busting:
Dangerous – Vehicle Traffic
 Studies of intersections around the U.S.
that have been converted from stop signs
or traffic signals to modern roundabouts:
− Total crashes were reduced by 39%
− Serious crashes were reduced by 76%
− Fatal or incapacitating injuries reduced by 89%
− Reduced conflict points
Roundabout Myth Busting:
Dangerous – Vehicle Traffic

Conflict points are reduced and those remaining are at low
angles

Slower speeds mean crashes are usually completely avoided
and actual crashes are minor at worst
32 Conflict Points
•High-speed
•High-angle
•High-energy
8 Conflict Points
•Low-speed
•Low-angle
•Low-energy
Roundabout Myth Busting:
Dangerous – Vehicle Traffic
 Icy conditions
− Hazardous for any intersection type
− T-bone type crashes are virtually eliminated
 Designer’s personal experience
− Smattering of minor crashes
− No injury or fatal crashes
Roundabout Myth Busting:
Dangerous – Pedestrian & Bicycle
Traffic

Lack of meaningful statistic set
−
Nothing pointing to increased or decreased
risk




Reduced conflict points
Cross one direction of traffic at a time
Slower vehicle speeds
Shorter distance to a refuge area

Crossings pulled back to allow focus from
driver on crossing prior to focus on
yielding
Visually impaired issue

−

Pedestrian activated signal system a
possible solution when warranted
Designer’s personal experience – crossings
require special attention to location and
visibility
Roundabout Myth Busting:
Roundabouts are More Expensive
 Case by case when compared to signals
 When completely reconstructing an
intersection roundabouts are often cheaper
 Partial/widening may favor signals
 Annual maintenance can be less depending
on level of landscaping
 Roundabouts and signals are generally
comparable
Roundabout Myth Busting:
Large Vehicles Can’t Navigate
 Roundabouts are designed
based on large vehicle
movements
−
Truck aprons allow rear
wheel tracking
−
Wider outside radii
−
AutoTURN software used to
check design
 Special design vehicles can
be accommodated
 House moving routes have
been accommodated
Roundabout Myth Busting:
Emergency Vehicles Will Be Hindered
 Large fire truck will fit
 Crash in roundabout
will most often not
block passage
 Driver expected to
clear intersection just
like at other types
 No opportunity for
pre-emption
Roundabout Myth Busting:
Difficult to Maintain
 Maplewood & Cottage Grove have little
trouble plowing
 Maintained jointly in Cottage Grove with
MnDOT
 Access to central island for routine
maintenance
 No maintenance of signals
Roundabout Myth Busting:
Lower Capacity than Signals
 Almost always comparable to signals –
often higher capacity with lower average
delays
Mn/DOT
WisDOT
Roundabout Myth Busting:
Longer Delays than Signals
 Frequently provides lower average delays
 Case-by-case
Roundabout Myth Busting:
Only a Traffic Calming Tool
 Often higher capacity and lower delays
compared to signals while providing greatly
improved safety performance
Roundabout Myth Busting:
Being Removed on East Coast Because
They Don’t Work
 The ones being removed are not “modern”
roundabouts
 In many cases the replacement is a roundabout
Roundabout Myth Busting:
Not for High-Speed Roads
 The second principle of a
“modern” roundabout is
geometric curvature to
control speeds
 Additional splitter island
lengths and gradually
slower curves
approaching may be
implemented
 Signage and lighting are
keys
Modern Roundabout
Characteristics
 Yield at entry
 Traffic
deflection
 Geometric
curvature
 Counterclockwise
circulation
Driving Roundabouts
 Yield to traffic in the roundabout
 Always proceed to the right around the center
island, never to the left
 Exit to the right onto your chosen street
Benefits of Modern
Roundabouts
 Increased safety
−
Up to 75% accident reduction
−
Reduced crash severity
 More capacity than signal-controlled intersection
−
30%-50%
 Self-regulating
 Shorter traffic delays than signal-controlled
intersection
 Lower maintenance compared to traffic signal
Benefits of Modern
Roundabouts
 Improved aesthetics
University Place, WA (Before)
Benefits of Modern
Roundabouts
 Improved aesthetics
University Place, WA (After)
Pedestrian Safety
 Lower vehicle speeds
 Crossing located about one vehicle length
before the vehicle yield line
 Splitter island can act as a refuge
 Concentration is on one conflict at a time
Typical Pedestrian Crossing