Traffic patterns in the United States are increasingly decentralized. Suburb to suburb commute
has been the most common type of commute since the 1970s (1). This commute includes work
trips, shopping trips, and recreational trips. The road system is not well equipped to handle this
type of commuting. Circulatory highways, like beltways, and a few local roads needs to carry a
very large portion of the suburb-to-suburb commuting traffic.
Due, in part, to the changes in traffic behavior, many intersections do not accommodate some
common traffic patterns very well. Heavy turning movements are often a problem at
intersections. Many intersections now need three lanes for left or right turns, which can cause
safety and operational problems. Some of these intersections need to be grade-separated, which
can be costly. When there is heavy directional movement in more then one direction, most
intersections have difficulties accommodating the traffic. If the heavy movements are both ways
along the same road, there are often synchronization problems with other signals on the road.
The intersection designs are also engineered for a strong hierarchy of intersecting roads. For
example, an arterial road normally intersects collector roads at signals. However, there are many
cases where the two heavily utilized arterials or intersect, which makes designing intersections
and interchanges even more difficult.
The purpose of this paper is to introduce two new designs, developed by the author, which can
accommodate the traffic patterns at major intersections and interchanges. The intersection design
is called the “synchronized-split phasing intersection”. The interchange design is called the
“diverging diamond interchange”. These designs take advantage of the benefits of split-phasing
Some of the characteristics of the synchronized split-phasing design are similar to the continuous
flow intersection (2). The flow of traffic is dispersed before the main intersection. However, the
continuous flow allows left turning movements to cross over before the main intersection,
whereas the synchronized split-phasing design allows both left and through movements to
crossover. Different benefits in signal timing and phasing coordination are made with each
design.