RIRO expressway

Right-in/right-out (RIRO) and left-in/left-out (LILO) refer to a type of three-way road intersection where turning movements of vehicles are restricted. A RIRO permits only right turns and a LILO permits only left turns. "Right-in" and "left-in" refer to turns from a main road into an intersection (or a driveway or parcel); "right-out" and "left-out" refer to turns from an intersection (or a driveway or parcel) to a main road. RIRO is typical when vehicles drive on the right, and LILO is usual where vehicles drive on the left. This is because minor roads usually connect to the outsides of two-way roads. However, on a divided highway, both RIRO and LILO intersections can occur.

The remainder of this article refers only to RIRO but applies equally to LILO.

A RIRO intersection differs from a 3/4 intersection (right in/right out/left in) and an unrestricted intersection.

RIRO is an important tool of access management, itself an important component of transportation planning. A study applying access management guidelines to the redesign of Missouri Route 763 in Columbia, Missouri illustrates how RIRO, combined with signalized intersections designed to permit U-turns, can accommodate high volumes of traffic with low delay and high safety.

The RIRO restriction typically is enforced through physical barriers such as a traffic island in an intersection to direct vehicles into the permitted turn, and to restrict vehicles from traveling through the intersection. The major road itself often has a median separating the two directions of traffic. The restriction may also be achieved by signage, but when a median or other barrier is not present in the median of the major road, RIRO configurations have been found to result in significant violation rates.

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Wikipedia