Rotary (intersection)

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A rotary is a type of circular roadway intersection.

Most common in the Northeastern United States and often referred to in common usage as a traffic circle outside New England, a rotary is primarily a mid-twentieth-century roadway design defined as a circular, one-way, often multi-lane roadway, similar to a traffic circle or a roundabout, but with key differences. They often serve as overpasses or underpasses to limited-access expressways (See Roundabout interchange). Entry to the rotary is typically controlled by yield signs, but at some locations, circulating traffic may be required to yield to entering traffic in order to minimize delay to high-volume entries.

[edit] Rules of operation

Traffic already in the rotary typically has the right-of-way as is the case with a modern roundabout and opposite of a traffic circle, although there are exceptions. Rotaries tend to be much larger in diameter than roundabouts, and traffic entering the rotary traffic coming on or off does so primarily tangental to the circle, not on a curve. As a result, rotary traffic often travels at speeds in excess of 30 miles per hour, leading to confusion and accidents that the modern roundabout does not suffer from^[1].

Although rotary entries are usually controlled by yield signs, it is often possible to enter a rotary alongside circulating traffic due to ample roadway width or an added lane. Traffic entering a rotary normally must be positioned in the inner lane to remain in the circle beyond the first exit, and subsequently change lanes outwards in order to exit. This weaving of entering and exiting traffic within a short distance can lead to confusion, congestion and large differences in speed amongst circulating vehicles, which therefore contributes to crashes.

Unlike multi-lane roundabouts, rotaries typically do not allow exits from the inside lane. To reduce weaving, drivers are supposed to choose their entry lane based upon their desired path through the rotary, as is the case with a roundabout. However, unlike a roundabout, lane changes are typically allowed within a rotary. The driver's manual published by the Commonwealth of Massachusetts, where rotaries are more common than other regions, states the following:

If the rotary has a single lane, you must enter from the right lane of the road you are coming from and exit onto the right lane of the road you intend to travel on. If the rotary has multiple lanes, look for signs to help you choose the proper lane. If there are no signs, you should do the following:
• For a quarter-turn, or to continue straight ahead, enter the rotary from the right lane, stay in that lane, and exit onto the right lane.
• For a three-quarter-turn, or a U-turn, enter the rotary from the left lane, travel through the middle or inner lane, and exit onto the right lane. If coming from a road with a single lane, you should stay in the right lane for the entire turn. ^[2]

Although the term rotary is a fairly precise traffic engineering definition, many rotaries are called traffic circles or simply circles in popular usage, such as the Portsmouth Traffic Circle in New Hampshire.

[edit] Examples

U.S. Highway 1 at U.S. Highway 4 in Portsmouth, New Hampshire (Referred to locally as the Portsmouth Traffic Circle)
Airport Rotary, Iyannough Road at Barnstable Road in Hyannis, Massachusetts on Cape Cod
U.S. Highway 6 at Massachusetts Route 6A in Orleans, Massachusetts on Cape Cod
Weatherford Circle, U.S. Highway 377 at Texas State Highway 183 in Benbrook, Texas (Referred to locally as a Traffic Circle)

[edit] Gallery

In the U.S. state of New Jersey, rotaries are called traffic circles

Massachusetts Rotary signage. Note the Yield sign

The small Industrial Avenue rotary in Lowell, Massachusetts. This rotary joins the Lowell Connector with local streets. Note how straight the approaches to some of the ramps are.