Traffic circles are predominantly circular due to engineering principles that facilitate smooth traffic flow and minimize the need for constant speed and steering adjustments. The circular shape allows for efficient layout and has the smallest perimeter for a given area, making it optimal for traffic management. While some areas, like Cambridge, MA, feature non-circular traffic designs, these are exceptions rather than the norm. Other countries have experimented with various shapes for traffic circles, showcasing creativity in design. Ultimately, the circular traffic circle remains the most effective and widely used configuration for managing vehicular movement.