What Are the Types of Signalized Intersection?
Intersection types are classified according to the type of intersection of road users. There are two types intersections “Vehicle Intersections” and “Pedestrian Intersections”.
Intersections where vehicle-vehicle encounters are at the point of intersection. Vehicle- pedestrian encounters may also occur at such intersections, but it is classified as a vehicle intersection because vehicle volume is more intense and safety of these encounters at the intersection is at the forefront. Basically, these intersections are classified into four different types as three-armed, four-armed, rotary island and roundabout island intersections according to the number of branches at the intersection.
Three Branches Intersections
At intersections in this group, the angle between the arms is desired to be close to the right angle. For vehicles that will turn left at the junction, creating a pocket and storing the vehicles in the pocket has high importance for the safety and operational performance of the junction. The capacity of the intersection will be increased, if vehicles use roundabout islands while they turn right at the intersections. At such intersections, in the flash mode activated after the specified time at night, the secondary roads and turn pockets are operated with red flash and the main roads with yellow flash. Single signal head with right arrow can be red or yellow according to the intersection situation.
Four Branches Intersections
The intersections in this group are required to have the angle between the arms close to the right angle as in the three-arm intersections. Since there is too much current in this type of multi-branch intersection, directing the vehicles, which will change direction, to a channel, will prevent turmoil in the intersection and affect the performance of the intersection in a positive way. In order to ensure the safety of pedestrian crossings at these intersections, the creation of return islands and the absence of elements that obstruct the viewpoint is required. Depending on the volume of right-to-left rotation currents, speed regulating strips can be formed by adding auxiliary strips. In this type of intersections, in the flash mode activated after the specified time at night; secondary roads and turn front are operated by red flash. Single signal head with right arrow can be red or yellow based on speed limit in intersection and viewpoint.
Rotary Island Intersections
Rotary island intersections serve to intersection users in a different way than roundabout island intersections. The created island does not reduce the speed of the drivers and therefore, such intersections are operated with signal control. In this type of intersections, in the flash mode activated after the specified time at night; the secondary roads and inter-islands are operated by red flash and the main roads by yellow flash. Single signal head with right arrow can be red or yellow based on speed limit in intersection and viewpoint.
Modern Roundabout Intersection
It is a type of intersection which is indicated by signs that the traffic flow is directed around a central island and that the vehicles around the island have the right of first passage. In this type of intersections, the diameter of the island is kept high, the speed of the vehicles entering the intersection is reduced and the exist of the vehicles in the roundabout will be safe. In this type of intersections, in the flash mode activated after the specified time at night; secondary roads, main roads should be programmed with a red flash and the island inside should be programmed with a yellow flash.
Intersections which are only vehicle-pedestrian intersection. The purpose of the installation is to provide the pedestrians safe passage the points where pedestrian-vehicle conflicts are intense and pedestrian safety is endangered. Pedestrian speeds are the most important factors to be considered in project planning and programming. Signalized pedestrian intersections are divided into two as pelican and graded.
Pelican Pedestrian Crossing
They are the crossroads where pedestrians get the right to cross the road by stopping the traffic of the vehicle by pressing the button. It is recommended to apply at points where the road cross-section width is less than 12 m (TSE, 1990-1). However, where two-way road the cross-section width exceeds 12 m, the width of the central refuge width is less than 4 m, or on one-way roads where the central refuge is not existing, a pelican pedestrian crossing can applicable. Protective barriers should be maintained in the determination of pedestrian corridors and ensuring the safety of pedestrians waiting for the right of passage on the sidewalk. In addition, it is necessary to make pavement inclination in order to ensure the passage of disabled pedestrians using wheelchairs at the points where these junctions will be established. These inclinations should be created at a maximum inclination of 8% and a minimum width of 150 cm at the intersection of the pavement with the road. For visually impaired pedestrians, embossed surfaces should be applied at the intersection point.
Stepped Pedestrian Crossing
It is a pedestrian crossing applied on two-way roads where the pedestrian cross section is more than 12 m and the central refuge width is more than 4 m. It is also recommended that the pedestrian turnout area width to be applied in the central refuge should be at least 10 m. In such passages, the pedestrians are passed in two stages and the pedestrian passage axis is changed while the stage is formed. The pedestrian button must be pressed for each step transition. In addition to the safety measures applied to the pelican pedestrian crossings, the asylum area in the central refuge should be surrounded by barriers. For visually impaired pedestrians in the shelter area, embossed surfaces along the walking axis should be used. In this type of pedestrian crossing, the priority is to ensure pedestrian safety. Pedestrian crossing times are shorter, but waiting times are longer. For vehicles, the shorter pedestrian crossing time is applied in all directions, so waiting times are less than for the pelican pedestrian crossing. Green wave can be applied between intersection stages to reduce waiting time.