Channelization is a traffic engineering concept that employs the use of secondary roads, slip lane to separate certain flows of traffic from the main traffic lanes. The method came into favor in the United States in the 1950s. One of the most effective and efficient methods of controlling the traffic on a highway is the adoption of high intersection geometric design standards.
Channelization is an integral part of at-grade intersections to separate turning movements from through movements that are considered advisable. That helps greatly to reduce the intensity and frequency of loss of life and property from crashes. Proper channelization increases capacity, improves safety, provides maximum convenience, and instils driver confidence. Improper channelization has the opposite effects and may be worse than none at all.
Over-channelization should be avoided because it could create confusion and worsen operations. Channelization of at-grade intersections is the separation or regulation of conflicting traffic movements into definite paths of travel by the use of pavement markings, raised islands, or other suitable means to facilitate the safe and orderly movement of both vehicles and pedestrians.
Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads/sidewalks) for travel and transportation.
A roundabout, a rotary and a traffic circle are types 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.
An intersection or an at-grade junction is a junction where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections are often delineated by gores and may be classified by road segments, traffic controls and lane design.
Level of service (LOS) is a qualitative measure used to relate the quality of motor vehicle traffic service. LOS is used to analyze roadways and intersections by categorizing traffic flow and assigning quality levels of traffic based on performance measure like vehicle speed, density, congestion, etc. In a more general sense, levels of service can apply to all services in asset management domain.
The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway design and construction throughout the United States. Despite its name, the association represents not only highways but air, rail, water, and public transportation as well.
Highway 91 is an alternative freeway route to Highway 99 through Delta, New Westminster and Richmond, British Columbia. The highway was built in two sections, the first section from Delta to East Richmond in 1986, and the second section across Richmond in 1989.
A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.
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.
Road surface marking is any kind of device or material that is used on a road surface in order to convey official information; they are commonly placed with road marking machines. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses. In some countries and areas, road markings are conceived as horizontal traffic signs, as opposed to vertical traffic signs placed on posts.
A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the interchange so that traffic crossing the freeway on the overpass or underpass is operating on the opposite driving side from that which is customary for the jurisdiction. The crossovers may employ one-side overpasses or be at-grade and controlled by traffic lights.
In the field of road transport, an interchange or a grade-separated junction is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, using a system of interconnecting roadways to permit traffic on at least one of the routes to pass through the junction without interruption from crossing traffic streams. It differs from a standard intersection, where roads cross at grade. Interchanges are almost always used when at least one road is a controlled-access highway or a limited-access divided highway (expressway), though they are sometimes used at junctions between surface streets.
A junction is where two or more roads meet.
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 enable access to land uses while maintaining roadway safety and mobility through controlling access location, design, spacing and operation. This is particularly important for major roadways intended to provide efficient service to through-traffic movements.
A quadrant roadway intersection adds an additional "quadrant roadway" between two legs of an intersection. This roadway adds two three-way intersections in addition to the original four-way intersection, moving all left turns or right turns from the main intersection. The design is intended to improve traffic flow by reducing signal timing phases from four to two in the main intersection. The design is intended for intersections where large artery routes meet in an area of dense development and high pedestrian volume.
Intersection Capacity Utilization (ICU) method is a tool for measuring a roadway intersection's capacity. It is ideal for transportation planning applications such as roadway design, congestion management programs and traffic impact studies. It is not intended for traffic operations or signal timing design. ICU is also defined as "the sum of the ratios of approach volume divided by approach capacity for each leg of intersection which controls overall traffic signal timing plus an allowance for clearance times." The ICU tells how much reserve capacity is available or how much the intersection is overcapacity. The ICU does not predict delay, but it can be used to predict how often an intersection will experience congestion.
The Highway Capacity Manual (HCM) is a publication of the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine in the United States. It contains concepts, guidelines, and computational procedures for computing the capacity and quality of service of various highway facilities, including freeways, highways, arterial roads, roundabouts, signalized and unsignalized intersections, interchanges, rural highways, and the effects of mass transit, pedestrians, and bicycles on the performance of these systems.
A seagull intersection or continuous green T-intersection is a type of three-way road intersection, usually used on high traffic volume roads and dual carriageways. This form of intersection is popular in Australia and New Zealand, and sometimes used in the United States and other countries.
In transportation infrastructure, a bidirectional traffic system divides travellers into two streams of traffic that flow in opposite directions.
Sidra Intersection is a software package used for intersection (junction), interchange and network capacity, level of service and performance analysis, and signalised intersection, interchange and network timing calculations by traffic design, operations and planning professionals.
Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.
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