Right-in/right-out (RIRO) and left-in/left-out (LILO) refer to a type of three-way road intersection where turning movements of

vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...

s 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 A driveway (also called ''drive'' in UK English) is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group. Driveways rarely have traffic lights, but some that bear ...

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 Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes referred to ...

, 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 A dual carriageway ( BE) or divided highway ( AE) 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 ...

, 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. Rotor Zagreb-crop

Design

RIRO is an important tool of

access management Access management, also known as access control, when used in the context of traffic and traffic engineering, generally refers to the regulation of interchanges, intersections, driveways and median openings to a roadway. Its objectives are to en ...

, itself an important component of

transportation planning Transportation planning is the process of defining future policies, goals, investments, and spatial planning designs to prepare for future needs to move people and goods to destinations. As practiced today, it is a collaborative process that ...

. 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-turn A U-turn in driving refers to performing a 180° rotation to reverse the direction of travel. It is called a "U-turn" because the maneuver looks like the letter U. In some areas, the maneuver is illegal, while in others, it is treated as a ...

s, 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 A traffic island is a solid or painted object in a road that channels traffic. It can also be a narrow strip of island between roads that intersect at an acute angle. If the island uses road markings only, without raised curbs or other physica ...

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 epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seatbelt use) at a specific time. It is derived by comparing the number o ...

in the state of

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

, although they are not limited to that state.

Use

RIRO road configurations are an important tool for

. General types of RIRO road configuration include

limited access road A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, limited access freeway, and partial controlled access highway, is a highway or arterial road for high-speed traffic which ...

s (

s, etc.) and

roundabouts A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford Eng ...

. To travel in the restricted direction, vehicles must first turn in the permitted direction, then reverse direction in a

, by going around a roundabout or by going left around a

block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...

. RIRO is especially useful where left turns would require crossing in front of oncoming vehicles.

Safety

RIRO configurations generally improve

road-traffic safety Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, Driving, motorists, vehicle passengers, horse riders, and passengers o ...

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.

References

External links

Introduction to RIRO Expressways, OntHighways.com

{{DEFAULTSORT:Right-in right-out Transportation planning Road junction types Limited-access roads Controlled-access highways