Let’s begin with a scenario that could occur in any city or town across the country. A traditional, four-way intersection on the main road into a municipality’s downtown district has a higher-than-average crash rate, and residents have complained about high traffic speeds. Town leaders hire an engineer to study the problem and recommend a solution. After a comprehensive study, the engineer proposes the intersection be converted into a roundabout. Unfazed by the uncertain looks he receives for his suggestion, the engineer attends a meeting of the Town Council a week later to make his case for the conversion.

1. Roundabouts: A Round Peg in a Square Hole
Let’s begin with a scenario that could
occur in any city or town across the country.
A traditional, four-way intersection on the
main road into a municipality’s downtown
district has a higher-than-average crash rate,
and residents have complained about high
traffic speeds. Town leaders hire an engineer
to study the problem and recommend a
solution. After a comprehensive study,
the engineer proposes the intersection be
converted into a roundabout. Unfazed by the
uncertain looks he receives for his suggestion,
the engineer attends a meeting of the Town
Council a week later to make his case for the
conversion.
His report is met with skepticism from some
council members and members of the public
in attendance, who make their concerns
known: roundabouts are confusing and
unsafe, inconvenient for pedestrians, and
expensive when compared to traditional
intersections. Some even make half-joking
references to Clark Griswold (of National
Lampoon’s fame) driving hysterically around
the roundabout near Big Ben in London.
The engineer explains the accuracy of growing
data in support of roundabouts and how they
moderate vehicle speeds, minimize conflicting
vehicle and pedestrian movements, reduce
the incidence and severity of crashes, and
can aesthetically enhance an area, while
increasing road system performance. Though
acknowledging a roundabout is potentially
more expensive, the engineer details how
the benefits outweigh the costs and explains
that some funding programs do exist to cover
portions of a roundabout’s construction cost.
In the end, the council backs the engineer’s
expertise. A few residents remain concerned,
but reserve further judgment. The town
builds the roundabout, the intersection’s
safety record improves, the speeding
complaints dwindle, and community members
grow accustomed to the change – their
suspicions displaced by acceptance born out
of familiarity and performance.
Why the resistance? The easy answer
is because that is how it’s always been. We
have grown comfortable with a traffic control
system governed by automated signals –
third-party referees who tell us when to
stop, when to go, and when to yield. We
motorists don’t even necessarily have to
think that much, we just react; an increasingly
dangerous proposition as our roads fill with
ever more passive and distracted drivers.
This tendency to passivity and distraction is
especially hazardous at the most dangerous of
traffic environments, the intersection.
The Federal Highway Administration (FHWA)
estimates there are 300,000 signalized
intersections in the United States. About
one-third of all intersection fatalities occur
at these locations, amounting to roughly
2,300 people killed each year. Furthermore,
Concepts
Fishbeck, Thompson, Carr & Huber, Inc.
Spring 2013
onceptsC
Diverging 9
Merging 8
Crossing 16
33
Diverging 4
Merging 4
Crossing 0
8
Standard
Intersection
Potential Vehicle Conflict Points
Roundabout
Roundabout Safety Statistics
• 38% reduction in all crash severities
• 75% reduction in injury crashes
• 90% reduction in fatal crashes

2. www.ftch.com/concepts
There are only three rules for modern roundabouts:
1) Traffic moves counterclockwise.
2) Entering drivers yield to circulating traffic.
3) Stay in your lane.
This keeps traffic in the circle moving
safely and contributes to a roundabout’s
capacity and effectiveness.
about 700 people are killed annually in
red-light running crashes. It is precisely this
danger that has given rise to the FHWA’s
effort to promote proven safety measures at
intersections.
Roundabouts are one such measure. The
FHWA says roundabouts have demonstrated
substantial safety and operational benefits
compared to most other intersection forms
and controls, with especially significant
reductions in fatal and injury crashes. In
addition, they can be an effective tool for
managing speed and creating a transition
area that moves traffic from a high-speed to a
low-speed environment.
Why are roundabouts safer than
traditional intersections? The one-
word answer is geometry. Roundabouts
reduce the number of places one vehicle
can strike another by a factor of four and do
away with the left turn movement against
oncoming traffic (arguably one of the most
dangerous turning movement conflicts,
resulting in severe T-bone crashes). Also,
since modern roundabouts do not have
traffic signals, they eliminate the scenario
where a motorist speeds up to beat the
red light. Drivers must slow down to enter
a roundabout because traffic is directed
around a center island, which also serves to
reduce vehicle speeds. These lower vehicle
speeds translate to overall intersection safety
– the number and severity of crashes drops
dramatically.
There is another factor that contributes to
the safety of roundabouts: watchfulness.
Drivers tend to be cautious when approaching
and driving through a roundabout because
it does not, initially, feel as comfortable as
a signalized or stop-controlled intersection.
This feeling can produce a heightened
awareness of our surroundings; the benefits
of which are obvious when compared to
the passive distraction we all witness during
our daily commutes. Roundabouts actively
engage drivers, relying on their ability to
assess changing traffic conditions and make
reasonable decisions.
Significant design elements of a
roundabout include a central circulation
island and splitter islands on each approach.
Safe pedestrian crossings can be integrated
into the splitter islands. Many roundabouts
are also designed with a truck apron, a raised
section of pavement around the central
island that acts as an extra lane for large
vehicle turn paths. The back wheels of the
oversized vehicle can ride up on the truck
apron so the truck can easily complete the
turn, while the raised portion of concrete
discourages use by smaller vehicles.
With a truck apron, roundabouts can
accommodate vehicles of all sizes,
including emergency vehicles, buses,
farm equipment, and tractor-trailers.
The central island can also be designed
and landscaped to allow emergency
vehicles to traverse the center in extreme
emergencies.
Public education is a critical, yet often
overlooked, aspect to successful roundabout
implementation. Many municipalities are
setting aside resources for informational
campaigns to teach their communities about
roundabouts. These campaigns include
mailings, brochures, online videos, and public
forums.
There are few cure-alls when it comes to
intersection safety, and roundabouts are not
always the best solution. Some intersections do
not have the right characteristics to consider a
conversion. However, if designed properly and
implemented effectively, roundabouts offer
one of the safest, most efficient, and elegant
alternatives to traditional intersection control.
Points to ponder the next time you’re stuck at
an empty intersection waiting for the signal to
change.
Arrows show
the direction
of traffic flow
Approaching traffic
slows and yields to
traffic in the circle
Pedestrians cross at
designated locations
Circulatory
Roadway
Central Island
Yield Line
Inscribed Circle
Diameter
Landscape
Buffer
Truck Apron
Entry
Exit
Accessible
Pedestrian
Crossing
Splitter
Island
Roundabouts are easy to use
For more information regarding roundabouts,
please contact Chris Sikkema, P.E.
cjsikkema@ftch.com.