****************************************** http://www.fhwa.dot.gov/rnt4u/ti/roundabouts.htm A roundabout eliminates some of the conflict traffic, such as left turns, that cause crashes at traditional intersections. Because roundabout traffic enters or exits only through right turns, collisions that do occur typically are less severe than those at conventional intersections. A roundabout also is safer than a traffic circle or a rotary, both of which are larger and operate under different traffic rules.
The three safety design features of a roundabout are yield control of entering traffic; channelized approaches; and geometric entry curvature. These three features are key to the success of a roundabout, because they effectively decrease driving speed (typically to 48 kilometers per hour (30 miles per hour) or less). Unlike a traffic circle or a rotary, a roundabout's incoming traffic yields to the circulating traffic. This creates a safer driving environment than that of traditional intersections. ****************************************** http://www.tfhrc.gov/safety/00068.htm Roundabouts: An Informational Guide [Quotes from Chapter 1] "many large circles or rotaries were built in the United States. The prevailing designs enabled high-speed merging and weaving of vehicles. Priority was given to entering vehicles, facilitating high-speed entries. High crash experience and congestion in the circles led to rotaries falling out of favor in America after the mid-1950's. The modern roundabout was developed in the United Kingdom to rectify problems associated with these traffic circles. In 1966, the United Kingdom adopted a mandatory "give-way" rule at all circular intersections, which required entering traffic to give way, or yield, to circulating traffic. This rule prevented circular intersections from locking up, by not allowing vehicles to enter the intersection until there were sufficient gaps in circulating traffic. In addition, smaller circular intersections were proposed that required adequate horizontal curvature of vehicle paths to achieve slower entry and circulating speeds. These changes improved the safety characteristics of the circular intersections by reducing the number and particularly the severity of collisions. Thus, the resultant modern roundabout is significantly different from the older style traffic circle both in how it operates and in how it is designed" A roundabout is a type of circular intersection, but not all circular intersections can be classified as roundabouts. In fact, there are at least three distinct types of circular intersections: . 'Rotaries' are old-style circular intersections common to the United States prior to the 1960's. Rotaries are characterized by a large diameter, often in excess of 100 m (300 ft). This large diameter typically results in travel speeds within the circulatory roadway that exceed 50 km/h (30 mph). They typically provide little or no horizontal deflection of the paths of through traffic and may even operate according to the traditional "yield-to-the-right" rule, i.e., circulating traffic yields to entering traffic. . 'Neighborhood traffic circles' are typically built at the intersections of local streets for reasons of traffic calming and/or aesthetics. The intersection approaches may be uncontrolled or stop-controlled. They do not typically include raised channelization to guide the approaching driver onto the circulatory roadway. At some traffic circles, left-turning movements are allowed to occur to the left of (clockwise around) the central island, potentially conflicting with other circulating traffic. . 'Roundabouts' are circular intersections with specific design and traffic control features. These features include yield control of all entering traffic, channelized approaches, and appropriate geometric curvature to ensure that travel speeds on the circulatory roadway are typically less than 50 km/h (30 mph). Thus, roundabouts are a subset of a wide range of circular intersection forms. Key roundabout features include: . Yield control of entering traffic . Channelized approaches . Appropriate geometric curvature to slow speeds the negative aspects of rotaries or neighborhood traffic circles (hereafter referred to as "traffic circles") may be mistaken by the public for a roundabout. Therefore, the ability to carefully distinguish roundabouts from traffic circles is important in terms of public understanding. How then does one distinguish a roundabout from other forms of circular intersection? Exhibit 1-5 identifies some of the major characteristics of roundabouts and contrasts them with other traffic circles." [Pictures shown] ****************************************** ________________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Woelflein Sent: 12 September 2005 21:57 To: U.S. Metric Association Cc: U.S. Metric Association Subject: [USMA:34435] Off-topic: Roundabouts, was Re: Re: One way to metricate the USA Slideshow | Print at Home | Order Prints | Save to: My Yahoo! Photos or My Computer Click a photo to view a larger version on Yahoo! Photos. See links above for more options. The "rotaries" are going away, but in Nashua (and other cities or towns in NH) we are getting "roundabouts." They are smaller than traffic circles and a lot cheaper than traffic lights. The pictures show two of Nashua's newer roundabouts. "Paul Trusten, R.Ph." <[EMAIL PROTECTED]> wrote: We still have roundabouts in "New" England. We call them rotaries or traffic circles. But, thank goodness, they are being steadily eliminated. nashua-mainstreet newhamp2 newhamp5 John Woelflein The larger versions of these photos will be available until December 11, 2005 (90 days) Share your pictures with PhotoMail from Yahoo! Mail. Learn More Go to Yahoo! Photos
