The phrases Right-in/right-out (RIRO) or left-in/left-out (LILO) refer to a type of roadway intersection where in the minor street approach's ingress and egress are both restricted. The restrictions employed are just as the name implies: a RIRO prohibits vehicles from entering the intersection via any movement other than a right-turn; and a LILO only permits a left-turn entry. To exit, RIRO prohibits through or left-turns out; and LILOs only allow for left-turns.
The restrictions are typically enforced through geometric provisions such as a concrete island to direct vehicles into the right or left turns, as applicable; and to restrict vehicles from traveling through the intersection. The major roadway itself often has a median separating the two directions of mainline traffic. In situations where a median is not present along the mainline, RIRO and LILO configurations have been found to result in significant violation rates -- despite the geometric indications of the concrete island or any regulatory signing.
Typically, the use of a RIRO is prevalent in areas where vehicles drive on the right side of the roadway, and similarly LILO is most prevalent in areas where vehicles keep left. This is a result of how access points to minor streets are often on the outside of a roadway. However, both RIRO and LILO intersections exist along right-hand drive and left-hand drive roadways, particularly along bifurcation one-way roadways.
RIRO and LILO configurations generally improve the safety and efficiency of an intersection by reducing the number of conflict points between vehicles. However, motorists who wish ingress or egress a RIRO or LILO via a restricted maneuver must often use alternate locations to perform a U-turn maneuver so that they may travel in their intended direction. As a result, RIRO and LILO configurations may improve the safety and operations of an intersection while consequently worsening those very concerns at another intersection upstream or downstream.