Interchanges — South Carolina Permit Test

A Diverging Diamond Interchange (DDI) means left-turning vehicles do not have to cross the paths of approaching through vehicles.

Left turns across oncoming traffic cause many interchange crashes, so the design removes that conflict.

This eliminates the need for left-turning vehicles to cross the paths of approaching through vehicles.

In a DDI, cross-street traffic is shifted to the left side of the street between the signalised crossover intersections.

Drivers meeting a DDI for the first time may think they are on the wrong side and swerve back.

By shifting cross street traffic to the left side of the street between the signalized crossover intersections,

A Restricted Crossing U-turn (RCUT) intersection removes left-turn and through movements from the cross street.

Crossing or turning left across a busy main road is where the worst side-impact crashes happen.

The RCUT intersection differs from a conventional intersection by eliminating the left-turn and through movements from cross street approaches.

At an RCUT, a driver wanting to go left or straight turns right onto the main road and then makes a U-turn at a one-way median opening.

Drivers who do not know the pattern may try to cut across the median where no crossing exists.

To accommodate these movements, the RCUT intersection requires drivers to turn right onto the main road and then make a u-turn maneuver at a one-way median opening (shown as the red movement in this figure).

What does a Diverging Diamond Interchange remove for left-turning drivers?

Crossing the path of oncoming through traffic. Left turns across oncoming traffic cause many interchange crashes, so the design removes that conflict. South Carolina Driver's Manual, p.80: “This eliminates the need for left-turning vehicles to cross the paths of approaching through vehicles.”