16. RED LIGHT RUNNING
Preliminary estimates for 2001 indicate 200,000
crashes, 150,000 injuries, and about 1,100 deaths were
attributed to red light running.
This is down to around 800 deaths in 2010
The use of RLR cameras very controversial
25. Lane flow example
lane Flow Example
http://www.ourston.com/resources/webcams/halifax.ht
ml
What about signing?
26.
27. Traffic Circle vs. Roundabout
Kingston Traffic Circle Under Construction to become a Roundabout
28. Traffic Circle vs. Roundabout
Malta Roundabout superimposed on Latham Traffic Circle
Tangential Approach
geometry
vs.
Deflected Approach
geometry
Clearly defined exit
29. Traffic Circle vs. Roundabout
Johnson City Traffic Circle becomes Roundabout
R C
31. Quick Comparison:
Circle, rotary Modern Roundabout
40- 50 mph 15 – 25 mph
Speeds 65-80 km/h Speeds 25-40 km/h
Diameter > 60 meters Diameter < 60 meters
About 200 ft About 200 ft
High speed merge can Safer, low-speed,
be confusing and adequate deflection
Clear yield at entry
36. Pedestrian conflicts
Conventional intersections; potential vehicular
conflicts, each coming from a different direction:
1. Left turn, through and right turn movements from
the leg of the intersection the pedestrian is crossing.
2. Through movements coming from the opposite side
of the intersection.
3. Right turns from the cross street.
4. Left turns from the cross Street.
5. Right turn on red
41. U.S Single-Lane Roundabout Crashes- Insurance
Institute for Highway Safety (IIHS) Study Results
(IIHS) study [Persaud, et.al., 2001]
Highly significant reductions of approximately
40% for Overall Crashes
76% for Injury Crashes
90% for Fatal and Incapacitating Injury Crashes (predicted)
42. Using IIHS Figures
Roundabouts have:
Potential to save motorists:
Hundreds of thousands of injury crashes
Thousands of deaths
43. Benefits of a Roundabout
SAFETY, particularly injury crashes and fatalities
Including safer left turns (all right turns)
More efficient traffic flow
Increased capacity for given level of demand
Less vehicle air pollution
Pedestrian safety
Access management
44. Benefits of a Roundabout (Cont’d)
Community Benefits
Aesthetics/ Landscaping
Walkability/Village Atmosphere
Neighborhood Traffic Calming (secondary benefit)
Catalyst for Smart Growth
Lower life cycle costs at many intersections
46. Hutchinson, Roundabout
The Hutchinson News
“If you do build a roundabout it will be the ‘Mother of
all Bad Intersections’. We could sell tickets to see it.”
“They are easy to find; just look for a traffic jam and
the ground piled up with broken glass and car parts.”
CARS Organization
52. Safety problems correctable by
roundabouts
Right angle, head-on, left and through, and U turn
conflicts.
High crash severity – injury or fatal.
Sight distance or visibility problems that reduce the
effectiveness of stop sign control.
Inadequate separation of movements on some
approaches
Red light running
53. Statement from Discover Magazine
Around 2000 :“The modern roundabout may be the
safest most efficient traffic control device available
today.”
I say it is !
54. Caveats
Safety and efficiency achieved by a well designed
roundabout keys:
Deflection
Low-speed
Lane continuity
55.
56. Pedestrian Safety
Major studies have found no fatalities at US
roundabouts
Cross one lane at a time- single lane
Cross traffic going in one direction at a time.
Less likely to be killed at low speeds
Actually very little US data on pedestrian safety
Worldwide, roundabouts show increase in pedestrian
safety
61. Increased vehicle storage
(number of vehicles a function
of distance of exit lane crosswalk
from circulating lane. ) In VISSIM prelim results,
20, 60 100 vehicle storage for proximal, zig zg and distal
62. Visually Impaired
Access Board recommendations -Engineering judgment for
now; at least not enforceable standards
PROWAG ( Public Right of Way Accessibility Guidelines)
Blind difficulties: finding/aligning crossing, judging traffic
flow, evaluating gaps.
Issues at roundabouts
Wayfinding to set back crossing
Traffic flow sounds not clear
Gap Creation without stop condition
Gap Detection not as clear as at stop control
63. ADA and the Access-Board
Around 2000 declared roundabouts not accessible.
Draft language would have required pedestrian signals
on all legs of all roundabouts.
Later drafts require pedestrian signals on all legs of
two or more lane roundabouts.
Have indicated all along that full, green, yellow, red
signals not necessarily required
A-B latest language OKs HAWK (pedestrian hybrid
signal )– or equivalent control that will make
roundabout crosswalks accessible to blind
pedestrians. ???????
68. KSU Roundabout Performance
The primary focus of this research was to study the
operational performance of 11 Kansas roundabout s
The research focused on eleven sites with different
traffic volume ranges where a modern roundabout has
replaced or built instead of a Stop or Signal controlled
intersection
69. KSU Studies contd..
Results of studies for Kansas DOT at several
roundabouts indicate that the operational
performance of roundabouts is better than
TWSC, AWSC and Signalized intersections at all
locations studied
70. KSU Studies contd..
Helped to establish that even at relatively low traffic
volumes, modern roundabouts could be beneficial as a
traffic control device at an intersection
71. Kansas Average-Operational Performance
Measures Of Effectiveness Before R.A % Diff.
Average Intersection Delay
(Seconds/Veh) 20.2 8 -65%
Max Approach Delay (Seconds/Veh) 34.4 10.4 -71%
95% Queue Length (Feet) 190 104 -53%
Degree Of Saturation- Intersection (v/c) 0.463 0.223 -53%
Proportion Stopped- Intersection (%) 58 29 -52%
Max Prop. Stopped (%) 62 37 -42%
Before: Signal/AWSC/TWSC, RA: Roundabout
72. Emissions
Major pollutants
Carbon monoxide (CO),
Carbon dioxide (CO2),
Oxides of nitrogen (NOx),
Particulate matter (PM10 ,PM2.5)
Hydrocarbons (HC) or Volatile Organic Compounds
(VOC)
Modern Roundabouts cut emissions
74. KSU/IIHS Study- Delay & Proportion Stopped
Kansas, Maryland & Nevada
TWSC (Before) vs. Roundabout (After)
About 20% reduction in total delay
13% to 23% reduction in delay per vehicle
14% to 43% reduction in proportion stopped
75. ENERGY- Gasolene Usage
Another IIHS study of 10 signalized intersections:
If converted to roundabouts:
Each vehicle delay would be 1 minute less
Annual delay savings 325,000 hours
Fuel savings, 235,000 gallons/year
76. Bicycle conflicts
Conflicts experienced by bicyclists that roundabouts
are dependent on how they choose to negotiate the
roundabout. This is similar to conventional
intersections.
For experienced cyclist riding through the roundabout
conflicts are similar to those at signalized
intersections.
For those using the bike ramps and using the
crosswalk, complex or similar to those of a pedestrian.
A bicycle – pedestrian conflict is also possible.
USA experience with bicycles is very limited.
80. Public Acceptance
Generally poor- initially
Confusion with
Old circles, rotaries
Sometimes small circles
Heard or experienced lots of bad things about large,
old circles
Lots of misinformation “out there”- roundabout
myths, I call “irrational opposition”
Don’t like change
Don’t like speed control (small circles)
81. Public Acceptance Improves With
Experience
Survey by IIHS
Feeling about Roundabouts
BeforeAfter
Strongly/Somewhat Favor 31% 63%
Strongly/Somewhat Oppose 55% 28%
82. Conclusion
At most intersections with significant cross traffic and
turning movements the modern roundabout is the
safest most efficient form of intersection control
available today.
After construction attitudes change to more positive
Public needs more education
84. Flannery (2000) Study of Roundabout Crashes
Main Causes:
1. Approach geometry allowing high speed, and
2. Lack of adequate deflection in the roundabout
85. New Zealand Safety Audit Study
(Most common problems)
One of the most common:
Inadequate deflection as motorists
approach the intersection
87. Gyratory Operation- around1900
Eugéne Hènard, “Giratoire-boulevard” Place Ch.
d’Gaulle (1907)
Wm. Phelps Eno, Columbus Circle (1904)
S.J. Hellier, Great Britain (1901) suggested a gyratory
road system
(history continued)
88. London, Gyratory Systems introduced, 1925-26
One way systems around existing squares
“circus” idea (Brown)
“gyratories,” “rotaries,” “traffic circles”
(history continued)
89. Driver education
SLOW DOWN
Watch for pedestrians
Single lane- should be no problem
Multilane- get in right lane on entry !
Design should provide lane continuity.
At traditional intersection, Most drivers would not turn
right from the left lane or change lanes in the intersection
or anywhere without looking, signaling and finding a
gap, BUT MANY DO IT IN ROUNDABOUTS ! WHY ??
I believe drivers losing respect for YIELD everywhere
90. Great Britain roundabout development to 1966
Worked poorly-large queues, locking
Bigger and bigger designs – weaving
Did not end jams
Compromised safety
Intolerable by 1966
Almost gave up on them
(history continued)
91. Give Way Rule (Yield at entry), 1966
Ended locking
Improved capacity
Reduced crashes
Total change in design philosophy
(history continued)
92. US History
Massive road building in 1930’s
Gyratory intersections generally called “traffic
circles” were no advantage
Lost favor
By 1950’s no longer considered viable
Several “bad” circles still exist
(history continued)
93. Early US Designs
Large
Priority at entry
High speed entry
Weaving in circle/confusing
High crash rates
Important re-current acceptance
(history continued)
94. Great Britain, Post 1966
1975, revised design guidelines
Introduced concept of “deflection”
Islands at entry (splitter islands, generally
raised ) and central island
(history continued)
95. 1984, Design Standards about like todays
Entry path curvature standards
Concept of newer, smaller roundabouts as a
“normal” roundabout
Prefer modern roundabout
Could say 1984 was birth of the modern
roundabout world wide
(history continued)
96. US Modern Roundabout Growth
First in early 90’s
90 in 1995
About 3000-4000 today
In Kansas: ONE in 1997; about 175 today in operation,
being built or planned.; 6 on major state highway
intersections.
(end history)
97. Conclusions
Statistically significant reductions in
delay, queueing, stopping and emissions
At most intersections with cross traffic and turning
movements – a modern roundabout is the most viable
alternative for safe, efficient vehicular
traffic, especially for reducing injury crashes and
deaths !
In new areas, after construction public attitudes
change to more positive
Public needs more education
98. My Belief
Roundabouts are the safest most
efficient form of intersection traffic
control available today !