Don roundabouts need to be huge, like Dupont Circle in Washington D.C.?
Not at all! All four proposed Embarcadero roundabouts will fit into existing intersections in existing public rights of way. Modern roundabouts, such as are proposed for Embarcadero Road are far smaller than old rotary designs (like Dupont Circle or many others in New England, Europe and elsewhere). The old, large, high-speed traffic circle designs have a well-deserved reputation for driver confusion, congestion and high accident rates. In these old circles drivers typically circulate at 30 to 35 mph. Entering drivers approach at speed, and must cross exiting traffic in making a high-speed merge. With such high speeds, drivers need large gaps to be able to enter safely: this limits capacity severely. By contrast, modern roundabouts, with small diameters and carefully designed entry angles, provide a slow speed environment where drivers can and do select very small gaps, often as low as one second. It is this ability to make use of every small gap, and allow vehicles to enter simultaneo
