Cambridge's second new traffic rotary within two weeks will be constructed in Quincy Square opposite Lamont Library and the Union.

"Work is about to begin," Public Works Superintendent Ralph Dunphy confided yesterday. "It is another item on our list of projects to make Cambridge more attractive."

The new rotary, complete with flowers and grass, will have a 35-foot diameter. Cambridge police pointed out that it will greatly ease the flow of Massachusetts Avenue traffic as well as reduce the danger of collisions at the five-street intersection. Resurfacing work will continue down into Harvard Square.

Mass. Avenue's cobblestones will disappear, along with the tracks of the trolley line replaced last year by busses. The Avenue's corrugated surface has rocked vehicles for over 30 years; the new topping of bituminous concrete will result in smoother riding.