GOING AROUND IN CIRCLES.

It's been Instalanched. Read Tom Vanderbilt's column about modern rotaries.

Why are Americans so suspicious of roundabouts? The simplest answer is that we have grown used to (and feel comfortable with) binary, on-off traffic control. We suspect such signals are more efficient than the "fuzzy logic" that seems to govern roundabouts. Roundabouts require drivers to make their own decisions and assess others' actions, rather than relying on third-party signals.

Relying on third-party signals? There's debate in Illinois about whether red-light cameras should be used to enforce Right. Turn. On. Red. After. Stop. Many flatlanders treat a red light as an opportunity to roll into the turn, and they can often get away with it because of slow driver response to a red turning green, or because often there is no right arrow at a crossing with a dedicated left. You're halfway to a roundabout ...

You are in a modern roundabout if it is the entering driver who must yield to traffic already circling. You are not in a modern roundabout if you are expected to yield to entering drivers or if you encounter traffic lights or stop signs. Size is another easy distinguishing mark. The old traffic circles were huge, and actually required drivers to make fairly significant detours around a vast central area—typically just an expanse of desultorily tended grass. Roundabouts are typically half the size; some, like one in Kingston, N.Y., were built inside the infields of existing traffic circles. Rather than simple lawns, their centers may contain statues, beds of flowers, or any number of visual elements. Velocity is another telltale identification mark. The older traffic circles are often marked by high "entry speeds"—drivers come blazing in on long arcing curves and must then merge, highway-style. In the tighter spaces of the modern roundabout, the entrances and exits are "flared" with "splitter islands" that "deflect" incoming traffic.

In plain language, it's called moving the curbs back and perhaps planting a statue or something in the middle of the intersection to designate that it's a rotary.

Roundabouts are safer than traditional intersections for a simple reason: By dint of geometry and traffic rules, they reduce the number of places where one vehicle can strike another by a factor of four. They also eliminate the left turn against oncoming traffic—itself one of the main reasons for intersection danger—as well as the prospect of vehicles running a red light or speeding up as they approach an intersection to "beat the light." The fact that roundabouts may "feel" more dangerous to the average driver is a good thing: It increases vigilance. It's unlikely the average driver killed or severely injured in a high-speed "T-bone" crash as they drove through a green light felt much risk. In addition, drivers must slow to enter a roundabout: Placing an obstacle in the center makes this not only a physical necessity but visually disrupts the speed-encouraging continuity of the street.

That speed-encouraging is a consequence of ill-timed dashes to get to the next light, dashes often encouraged by all the slow-thinking shopping-cart drivers that will block your way at the next signal.

People may see vehicles winding slowly through a roundabout and think the intersection must be 1) adding to congestion and 2) slowing down people's travel times. But travel speed at any given moment should not be confused with overall travel time. Drivers may breeze through one intersection's green lights only to sit through a 90-second cycle at the next. What's more, the "protected turning movements"—i.e., the green arrows—required at many intersections steal time from the larger numbers of people wanting to proceed in every other direction. Roundabouts slow but rarely stop traffic. A noteworthy example here is Golden, Colo., which in 1999 converted a series of four formerly signalized intersections to roundabouts on a wide section of arterial highway that was becoming a major corridor for "big box" retail. While speeds between the intersections fell to an average of 37 mph from 47 mph, the time to travel the entire stretch of road dropped.

Might be cheaper than synchronizing the traffic lights, the Cold Spring Shops recommended practice. (The absence of synchronization is most annoying precisely at those commercial strips. First there's a light where the mile roads cross. Next the two-way stop where the mile road crosses the half-mile road becomes a four-way stop becomes a signal. Next come the retail developments, where the municipality may require the promoter to install additional signals, but not to time them.)