sentences:  Roundabout interchanges are much less common in North America but have been built more frequently since 1995, to improve safety, and to reduce traffic delays and bridge widening costs.However, many of the older and more dangerous rotary-style overpass interchanges have been signalized to improve throughput and safety, such as the former Drum Hill Rotary (now Drum Hill Square) in Chelmsford, Massachusetts, in New England, where such interchanges are unusually common.A divided diamond, in which the minor road is separated into four intersections, rather than two, also acts like a roundabout interchange, but it is more square in shape and, typically, has traffic light control.