Visual showing how diamond interchanges are used, with an expressway running across and a local road running in the center.
Left image is for left-side traffic (UK), right image is for right-side traffic (U. Large arrows show where turns are made; smaller arrows show traffic flow.
The freeway itself is grade-separated from the minor road, one crossing the other over a bridge.
Approaching the interchange from either direction, an off-ramp diverges only slightly from the freeway and runs directly across the minor road, becoming an on-ramp that returns to the freeway in similar fashion.
The two places where the ramps meet the road are treated as conventional intersections.
In the United States, where this form of interchange is very common, particularly in rural areas, traffic on the off-ramp typically faces a stop sign at the minor road, while traffic turning onto the freeway is unrestricted.
The diamond interchange uses less space than most types of freeway interchange, and avoids the interweaving traffic flows that occur in interchanges such as the cloverleaf.
Thus, diamond interchanges are most effective in areas where traffic is light and a more expensive interchange type is not needed.
But where traffic volumes are higher, the two intersections within the interchange often feature additional traffic control measures such as traffic lights and extra lanes dedicated to turning traffic.
The at-grade variant of the diamond interchange is the split intersection.
Because roundabouts can generally handle traffic with fewer approach lanes than other intersection types, interchange construction costs can be reduced by eliminating the need for a wider bridge.
This configuration allows other roads to form approach legs to the roundabouts and also allows easy U-turns.