Road & Street Intersection Layouts
Road intersections refer to the at-grade junction condition where two or more streets come together at a single location. Governed by turning regulations and augmented with traffic controls, signs, and lights, road intersections today are optimized based on daily traffic schedules and capacities. With cities transforming to become more walkable and inclusive of pedestrian and bicycle lanes, road intersections are increasingly tasked with managing and creating comfortable and safe moments of intersection between the many varied forms of traffic.
Factors to consider when planning a road intersection include: context, volume of traffic, speed of travel, and number of thru lanes and ways of crossing/turning. Road intersections can be uncontrolled (right-of-way), controlled (signalized), or manually controlled by traffic police.
The most common types of road intersections are four-ways, t-junctions, y-intersections, and traffic circles. A four-way is the most common type, often perpendicular, and involves crossing over two roadways. A t-junction is a three-way intersection when a minor roadway meets a major one. A y-intersection is similar to that of a t-junction except that all roadways are of equal size. A traffic circle is an intersection in which vehicles move around a central island in the same direction. Three or more roads will converge on the traffic circle.
A solid state controller is what controls traffic lights at road intersections. This controller typically consists of a power and interface panel, detectors, monitors, and an independent CMU acting as a fail-safe if a fault in the controller is detected. They are sometimes centrally controlled by computers for real time adjustment in accordance with traffic patterns. Traffic lights can often be found in a coordinated system, meaning signals turn green in a progressive manner for oncoming vehicles.