Right-in/right-out (RIRO) and left-in/left-out (LILO) refer to a type of road intersection where turning movements of vehicles are restricted. A RIRO permits only right turns and a LILO permits only left turns. RIRO is usual where 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.
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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[1] 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.
RIRO roads may also have grade-separated interchanges, but vehicles on these roads do not yield the right-of-way to other vehicles entering the roadway, nor encounter cross traffic. Such roads are sometimes called RIRO expressways. In the United States, they are sometimes called Jersey freeways, due to their prevalence in the state of New Jersey, although they are not limited to that state.
RIRO road configurations are an important tool for access management. General types of RIRO road configuration include limited access roads (divided highways, etc.) and roundabouts. To travel in the restricted direction, vehicles must first turn in the permitted direction, then reverse direction in a U-turn or by going around a roundabout. RIRO is especially useful where left turns would require crossing in front of oncoming vehicles.
RIRO configurations generally improve road-traffic safety and efficiency by reducing the number of conflict points between vehicles.
A RIRO configuration may improve safety and operations at one intersection while consequently worsening them at another intersection upstream or downstream.