Traffic Signal Control Systems
The primary and secondary purposes of a traffic signal control system.
A model for traffic flow that shows time on the x-axis and the space of the intersection approach on the y-axis.
What is a Time-Space Diagram?
A timing unit that controls one or more movements.
What is a Phase?
The minimum time that the display will remain green for a phase no matter what else occurs.
What is Minimum Green Time?
A traffic control system whose green interval and cycle length do not vary even as traffic demand varies.
What is a Fixed Time or Pretimed Signal?
The queueing model that considers deterministic arrivals, a deterministic service pattern, and one service channel.
What is D/D/1?
A diagram that defines which phases are compatible and can be timed concurrently.
What is a Conflict Matrix?
The maximum time that a detector can remain unoccupied before the passage timer expires.
What is Passage Time?
A system that responds to traffic demand by extending the green interval each time a new vehicle arrives on an approach.
What is an Actuated Signal?
A diagram that represents the flow rates of vehicles arriving at and departing from an intersection over time.
What is a Flow Profile Diagram?
A diagram that specifies the safe sequencing of phases at a signalized intersection.
What is a Ring Barrier Diagram (RBD)?
The maximum duration that the signal display will remain green after a call has been received on a conflicting phase.
What is Maximum Green Time?
The four components of a traffic signal.
What are the User, Detector, Controller, and Display?
A diagram showing the number of vehicles that have arrived at and departed from an intersection at any point in time during a cycle.
What is a Cumulative Vehicle Diagram?
A phasing scheme that serves each of the four intersection approaches in turn, often used when the intersection geometrics limit opposing left turn movements from traveling at the same time.
What is Split Phasing?
The type of phase termination that occurs when both the minimum green timer and the passage timer have expired.
What is Gap Out?
The three main performance measures considered when determining how well the desired outcome of a traffic signal is met.
What are Number of Stops, Delay, and Queue Length?
A plot of the queue length at any point in time or the vertical distance between the arrival and departure curves in a cumulative vehicle diagram.
What is a Queue Accumulation Polygon (QAP)?
The NEMA phasing numbers for left turns.
What are 1, 3, 5, and 7?
The type of phase termination that occurs when the maximum green timer expires.
What is Max Out?