Traffic Interchange

a junction of highways on different levels with ramps for the interchange of motor vehicles and other means of transportation from one road to another.

Figure 1. Diagrams of traffic interchanges: (a) cloverleaf interchange (intersecting), (b) Y interchange (connecting), (c) rotary interchange (branching)

Interchanges are built on highways of the first, second, and third technical categories. According to the relative positions of the roads, interchanges are divided into the following three groups: intersecting, connecting, and branching. Interchanges are also distinguished according to the way in which left turns are made: by means of a right turn (Figure l,a), a left turn (Figure l,b), or a left and a right turn (Figure l,c). Interchanges increase the traffic capacity of highways and improve the safety, flow continuity, and speed of traffic as compared with intersections on one level.

Interchanges are planned on the basis of studies of traffic flows in all directions, with the landscape and available free space being taken into account. Modeling of interchanges is often used for planning purposes, and speeds of 40–80 km per hour are assumed. The choice of the type of interchange to be used is made after a comparison of the alternatives with respect to technological and economic factors. The cloverleaf interchange (Figure l,a) is the most widely used type in the USSR and other countries. Cloverleaf interchanges are used, for example, on the Moscow Ring Highway. The development of traffic interchanges is associated with continuing improvements in traffic flow patterns.