People using the road make mistakes (like running stop signs and red lights), always have and always will. Crashes will always be with us, but they need not result in fatalities or serious injury.
Modern roundabouts are the safest form of intersection in the world - the intersection type with the lowest risk of fatal or serious injury crashes - (much more so than comparable signals). Modern roundabouts require a change in speed and alter the geometry of one of the most dangerous parts of the system - intersections. The reduction in speed and sideswipe geometry mean that, when a crash does happen at a modern roundabout, you usually need a tow truck, not an ambulance. Visit the Insurance Institute for Highway Safety for modern roundabout FAQs and safety facts. Roundabouts are one of several proven road safety features (FHWA).
The life saved may be your own.
Modern, slow and go, roundabout intersections have less daily delay than a stop light or stop sign, especially the other 20 hours a day people aren’t driving to or from work (it’s the #2 reason they’re built). Average daily delay at a signal is around 12 seconds per car. At a modern roundabout average daily delay is less than five seconds. Signals take an hour of demand and restrict it to a half hour, at best only half the traffic gets to go at any one time. 'At best' because traffic signals must have the yellow and all red portion (6+ seconds per cycle) for safety, and modern roundabouts do not. At a modern roundabout, drivers entering from different directions can all enter at the same time. Don’t try that with a signalized intersection.
First cost is the wrong way to compare projects. It would be like buying a car without knowing the fuel economy or safety of the thing, just its price to buy.
Present Value Life Cycle Cost Analysis (LCCA) is the best way to compare two or more choices. When comparing modern roundabouts to signals for a 20-year life cycle (the standard period), modern roundabouts usually cost less. Costs to compare include: first cost (design/land/construction), operation and maintenance (electricity, re-striping, upgrades, etc.), crash reduction (what’s your/your family’s safety worth?), daily delay (what’s your time worth?), daily fuel consumption (spend much on gas?), point source pollution (generated by stopped vehicles = health cost), area insurance rates (this costs more where it is less safe to drive). Each of these things, and others, can be estimated for any two choices and everyone near or using the project area will pay some portion of all these costs (and gain the benefits).
Many people confuse other and older styles of circular intersections with modern roundabouts. High speed, east coast rotaries, large multi-lane traffic circles (Arc D’Triomphe, Dupont Circle), and small neighborhood traffic circles are not modern roundabouts.
The Brits even call a merry-go-round a kid’s roundabout.
Go to http://www.k-state.edu/roundabouts/photos.htm to see pictures.
What is, and is not, a modern roundabout:
WA DOT: http://www.youtube.com/watch?v=vsCoI7lERGE
NJ traffic circles: https://en.wikipedia.org/wiki/List_of_traffic_circles_in_New_Jersey
NJ wins award for building roundabout:
BTW, safety projects traditionally qualify for 80% Federal reimbursement.
Mini-roundabouts are less common in North America, but frequently used in the UK. Their footprint is smaller, making them suitable for retrofit situations with right of way constraints (and lower cost). They are also commonly used where truck U-turns are not needed, so achieve all the safety benefits of compact modern roundabouts at a much lower cost. They are all truck apron, and in the UK are sometimes just paint on the road.
Single-lane modern roundabouts (50-120 feet in diameter) can handle intersections that serve up to 20,000 vehicles per day with peak-hour flows between 2,000 and 2,500 vehicles per hour. Two- and three-lane modern roundabouts (150-220 feet in diameter) can serve up to 60,000 vehicles per day and handle 2,500 to 5,500 vehicles per hour. Right-turn slip lanes can increase those numbers if needed (just like for signal intersections). Much depends on how balanced the entries are, but only in determining how many lanes are needed for each movement – just like at a signal controlled intersection.