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 ; "right-out" and "left-out" refer to turns from an intersection 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.
(Lower left) RIRO ramps on and off a divided highway connecting to the Remetinec Roundabout in Zagreb, Croatia.
A right-in/right-out intersection at the entrance to the National Institutes of Health along Maryland Route 355 in Bethesda, Maryland, United States.
King's Highway 11, looking north from overpass, toward South Sparrow Lake Road/Goldstein Road in Severn, Ontario, Canada. Several characteristics of a RIRO expressway are shown in the image: there is an unbroken median, there are right-in/right-out turns at the side roads, there are businesses with direct right-in/right-out frontage along the highway, and there is a sign indicating that access to the southbound lanes of the highway is via a right turn onto the side road (in this case, by following Goldstein Road to the overpass road, crossing over the highway, then continuing on the overpass road to South Sparrow Lake Road).
King's Highway 11, looking south from same overpass. In addition to the unbroken median, this image shows another characteristic of a RIRO expressway: direct right-in/right-out access to driveways (in this case, residential).
A dual carriageway (BrE) or a divided highway (AmE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways.
A typical British dual carriageway with central barrier on the A63 near Hull, England
Freeway of Route 25 between Tuluá and Andalucía, Valle del Cauca, Colombia. In 2014 there were 2,279 kilometers of dual carriageway highways in Colombia.
Clara Barton Parkway outside Washington, D.C.
Jersey barriers may be used to separate the carriageways where the space is narrow. See this example near Málaga, Spain. There is also a bus stop in the bottom-right corner of the picture; it would not exist in a motorway.