We recently posted an item about the advantages of roundabouts and how they differ from conventional intersections. In short, roundabouts eliminate conflict points, while increasing vehicle capacity; they reduce costs of traffic lighting; are safer for pedestrians; and the center islands can be attractively landscaped in an environmentally friendly manner. Read More
A roundabout is a circular intersection where traffic flows in a counterclockwise direction around a center island. Although they may look similar, roundabouts are not traffic circles or rotaries which may have stop signs, traffic signals, and higher speeds. Roundabouts allow traffic to flow through the intersection freely at slower speeds than the roadway. Drivers entering the roundabout yield to traffic inside the roundabout and adjust their speed to fit into gaps between vehicles.
Diverging-diamond (or double crossover diamond) interchanges (DDI) are like a remix of the traditional diamond interchange found at the intersection of interstates and highways. The first thing one will notice about the DDI is that traffic is routed to the left side of the road as it enters the DDI. Then as traffic leaves the DDI, it is routed back to the right side of the road. By moving the traffic to the left side of the DDI cars can make a “free” left turn onto the interstate. This turn is considered “free” because left-turning cars will not have stop or cross in front oncoming traffic once they enter the DDI. Right turns onto the interstate are still free as well because those cars can peel off to the right before entering the DDI. Because of these two free turning movements, DDIs allow traffic to move through the interchange more efficiently and quicker than through a traditional interchange. Less stop time and more go time also reduces vehicle emissions by reducing idle time.