Interchange Spacing. Interchanges should be located close enough together to properly
discharge and receive traffic from other highways or streets, and far enough apart to
permit the free flow and safety of traffic on the main facility. In general, more frequent
interchange spacing is permitted in urbanized areas. Minimum spacing is determined
by weaving requirements, ability to sign, lengths of speed change lanes, and capacity
of the main facility. Interchanges within urban areas should be spaced not closer than
an average of 2 mi (3.2 km), in suburban sections an average of not closer than 4 mi
(6.4 km), and in rural sections an average of not closer than 8 mi (12.9 km). In consideration
of the varying nature of the highway, street, or road systems with which the
freeway or expressway must connect, the spacings between individual adjacent interchanges
may vary considerably. In urban areas, the minimum distance between adjacent
interchanges should not be less than 1 mi (1.6 km), and in rural areas not less than 2 mi
(3.2 km).