If you need information about the types of road junctions then you came to the right place. Here we have discussed almost every type of road junction.
What is a Road Junction?
The engineering structures built in the areas where pedestrians and road vehicles meet on the same plane and pass each other’s route safely on highways in and out of the city are called Junctions. The main purpose of the junctions is to regulate the vehicle and pedestrian traffic on the main roads and secondary roads, as well as to increase the service quality of the junctions nearby.
Junctions, where two, three, or more roads intersect; are a traffic engineering design created to ensure the continuity of traffic flow and traffic safety, to eliminate negative situations such as decreasing the speed at traffic junctions, queuing caused by increased waiting, and the increase in operating costs that come with them.
Junctions include traffic flows at the road junction of two or more roads and the turns of these roads on top of each other. Many of these movements can be solved with geometric designs and controlled traffic, depending on the type of junction.
Regarding the arrangement of junctions:
- To prevent vehicles coming from different directions from colliding with each other,
- To minimize the effects of vehicles in different directions that will use the junction on each other in traffic,
- To reduce fuel consumption and loss of time caused by acceleration or deceleration,
- Ensuring sufficient time and space for safe passage to vehicles coming from different directions attention should be paid.
Road junctions are generally designed according to their density levels; On roads with low vehicle density, “at-grade (at-grade) junctions” are designed as “different-level” on roads with high vehicle density or where access is made in a controlled manner.
Here are the types of road junctions:
There are mainly two types of road junctions:
- At-Grade Road Junctions
- Crossroads with different levels
These two types are further subdivided which are explained below:
1. At-grade road junctions
The highway area, which is used jointly by traffic flows coming from different directions and converging at the same level, is called an “at-grade junction”. It is very difficult to design and build all the junctions at the junctions on a highway with different levels, even in countries with strong economies with large infrastructure investment budgets. For this reason, it is highly preferred that the majority of the junctions on highways in both urban and rural areas are designed and constructed equally.
Road Junctions by Number of Arms
Three-Leg Road Junctions
Three-arm T-type junctions are used on extra-urban roads with 2×1 lanes, where the traffic volume is low, as well as on urban 2×2 roads. Channeling is applied to control the revolving traffic and to adjust the sufficient turning radius in the junctions of the main road and side roads where the traffic volume is high (AASHTO, 1994).
Three-arm Y-type junctions are designed in places where it is not possible to make the junction with a right angle in cases such as zoning-expropriation problems on the side road, as they converge at a narrow-angle at the main road and side road junctions (Highway Design Handbook, 2005).
Four-Leg Road Junctions
In four-leg junctions, pockets are designed to reduce speed for turns on the main road (Highway Design Handbook, 2005). A pocket length of at least 60 meters should be applied to the joining lanes to be connected to the main road, while pockets of at least 45 m length should be applied to the separation lanes that will deviate from the main road.
Multi-Leg Road Junctions
In the case of five or more branches joining at-grade junctions, these junctions are called multi-leg at-level junctions. Such junctions are established in areas with low traffic density or where there is a stop notice (Highway Design Handbook, 2005).
Road Junctions According to Traffic Control Systems
Unsupervised Road Junctions
At uncontrolled junctions, warning signs and traffic signs are created to help drivers interact with other vehicles, so that the traffic continues healthily. One of the roads connected to the junction will be considered as the main road because it has more traffic volume than the other roads.
Controlled Road Junctions
For the drivers to understand clearly and clearly, in which order the traffic flow will take place at an uncontrolled junction, the junctions arranged by placing special illuminated equipment are called signalized or supervised junctions. Such junctions are used on roads with high vehicle density and generally in the city (AASHTO, 2011).
Another type of controlled junction is the roundabouts, which are formed by changing the operation style of the traffic at the junction as a result of the physical design of the junction in a different geometry, not with lighted electronic systems such as signaling. By the working principle of roundabouts, vehicles entering the junction have to significantly reduce their speed, although this reduces the capacity of the junction somewhat, it increases traffic safety at the junction (Highway Design Handbook, 2005).
2. Crossroads with Different Levels
Different level junctions can be made in different types. The number of roads connected to the junction, the density of the roads, and the road classes is the conditions that affect the way these junctions are built (Highway Design Handbook, 2005). Interchanges with different levels are specially designed to eliminate the collisions that may occur during crossing maneuvers and to minimize the number of collisions in turning maneuvers.
Three-Leg Road Junctions
Trumpet Road Junctions
‘Trumpet road junction’ can be applied where the three-leg road intersects. This type of junction can be designed at the points where low-density secondary roads connect to highways and at points where high-density highways and highways connect (AASHTO, 1994). These junctions, where all currents can freely perform their movements, are also economically logical designs as they require a single structure.
Half Clover Road Junctions
It is a type of junction where left-turning maneuvers in two directions are carried out with rotary ramps. In this type, which can be converted into full clover when necessary, it is possible to turn back on the secondary road (Highway Design Handbook, 2005).
Steering and Semi-Steering Road Junctions
These junctions are a type of junction that allows one or more left turns, or consists of ramps from the same or different levels in both directions. Multi-lane designs are also available. These designs are generally used at highway junctions or connections with the highway in urban environments (AASHTO, 2001).
Four-Leg Road Junctions
This type of junction is used in state or provincial road junctions where there is low traffic and where turn ramps are designed to the lowest standards due to variables such as topography, expropriation problem, culture, and nature (Highway Design Handbook, 2005).
Diamond-Diamond Road Junctions
This type is mostly a junction type that consists of the main road and four ramps in a parallel structure to this road and makes all turning maneuvers possible. For this type of joining and separation overlapping where no mesh overlap occurs, separating the storage lanes where the ramps meet the road and channeling the traffic as much as possible will increase the capacity and safety.
Clover Road Junctions
It is a multi-level junction type where collisions are eliminated in turns and loop ramps are designed for left turns and outer ramps for right turns (Highway Design Handbook, 2005).
It is a different level application of roundabouts within the at-grade junction types. It is a good alternative when the number of connecting arms is high and the number of vehicles making right, left and U-turns is high. Since the knitting movements are intense in these road junction types, the capacity decreases, thus limiting their use.
Steering and Semi-Steering Road Junctions
It is a high-quality junction type where connections are made with a diagonal geometry in the most suitable way for flow branches coming from all directions among different level junction types, and the braids are eliminated, where safety, capacity, comfort, and speed are all increased (AASHTO, 1990). These junctions, which are mostly designed on highways, are very costly due to the structures at different levels they have on them (Highways Design Handbook, 2005).
Single Point Interchanges
It is a different level junction type designed due to the restrictions imposed by expropriation and land use conditions. While the main road current continues uninterrupted in the design, the other branches intersect at a single point.
Different Level Road Junction Combinations
If one or two different turns have a higher traffic volume than the other turns, in such cases, it may be necessary to apply different junction designs in combination (Karayolları Design Handbook, 2005). This type of junction is generally used to connect high-standard roads in places where there are many industrial structures.