The extent of actuation is dependent on geometric and operational requirements, but is generally categorized as either semi-actuated or fully actuated. A pedestrian who is blind crossing parallel to that vehicle may not realize that a pedestrian phase is not provided during that vehicle's movement. Some actuated signals may provide very short phases to accommodate a single vehicle, without provision of a pedestrian phase during that cycle.Vehicular actuation allows the cycle to skip phases, so pedestrians with visual impairments cannot accurately predict, based on previous experience, when in the cycle the pedestrian phase will begin.Detectors are often placed on minor roads and in turn lanes to detect when a motorist is waiting to make a turn. Used where traffic volumes fluctuate or where it is desirable to minimize interruptions to traffic flow on the major street.Pushbuttons are most often used for pedestrian detection, though other "pedestrian sensing" technologies (microwave, infrared, piezoelectric) may be used as well.Detectors are most often inductive loops (electric), though they may be magnetic, microwave, video, and other detection technologies. Detectors monitor traffic and send signals to the traffic signal controller.Photograph of vehicle detector loop in pavementĪctuated signals change the length and/or order of the phases in response to variations in vehicle or pedestrian traffic. Still found in many locations, particularly in downtown areasįigure 3-2.Length of phases may change at different times of day, based on a consistent timing plan, for example, one street may have longer phases at peak hours than non-peak hours.Regularly repeated sequence of phases (often 30 seconds or more), regardless of traffic flow.Pretimed intersections operate in predetermined and predictable fashion. Larger, busier intersections will commonly have longer cycles.A cycle is timed from the start of one phase to the start of that same phase when it comes around again.
Although the MUTCD gives specific definitions to "phase" and "interval", these terms are often used interchangeably by traffic engineers.Ĭycle - sum total of all phases at a signal.When a major road intersects a minor road, the green intervals for the major road will be longer than those for the minor road to accommodate the heavier traffic on the major road. Busier intersections typically have separate phases for left turn movements (i.e., protected left turns).In other words, a phase is the time allotted to a specific movement, such as northbound traffic, whereas an interval is how long the light stays green, yellow, or red for vehicles or WALK, flashing DONT WALK, or DONT WALK for pedestrians.Interval - the part of a signal cycle during which signal indications do not change Phase - the right-of-way, yellow change, and red clearance intervals in a cycle that are assigned to an independent traffic movement or combination of movements There is some variability in timing plans in different municipalities and in different locations, depending on the roadway needs and local practices. It is important for O&M Specialists to understand the signal design and terminology to teach these concepts to their students. Timing plans may be of two general types:Ī signal at a given intersection may be designed to change from actuated to pretimed to flashing mode depending upon: Intersections are generally designed to provide optimal vehicle traffic flow. Intersection Signalization and Timing Plans Intersection signalization
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