Right-in/right-out (RIRO) andleft-in/left-out (LILO) refer to a type ofthree-way road intersection where turning movements ofvehicles 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 roadinto an intersection (or adriveway orparcel); "right-out" and "left-out" refer to turnsfrom an intersection (or a driveway or parcel) to a main road.[1][2][3] RIRO is typical when vehiclesdrive on the right, and LILO is usual where vehicles drive on the left. This is because minor roads usually connect to the outsides oftwo-way roads. However, on adivided 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 ofaccess management, itself an important component oftransportation planning. A study applying access management guidelines to the redesign ofMissouri Route 763 inColumbia, Missouri[4] illustrates how RIRO, combined with signalized intersections designed to permitU-turns, can accommodate high volumes of traffic with low delay and high safety.
The RIRO restriction typically is enforced through physical barriers such as atraffic 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 amedian 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.[citation needed]
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 calledRIRO expressways. In the United States, they are sometimes calledJersey freeways, due to theirprevalence in the state ofNew Jersey, although they are not limited to that state.
RIRO road configurations are an important tool foraccess management. General types of RIRO road configuration includelimited access roads (e.g.divided highways) androundabouts. To travel in the restricted direction, vehicles must first turn in the permitted direction, then reverse direction in aU-turn, by going around aroundabout, reversing direction at aninterchange with anoverpass orunderpass, or by going left around ablock. RIRO is especially useful where left turns would require crossing in front of oncoming vehicles.
RIRO configurations generally improveroad-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.[citation needed]
