An Introduction to Traffic Signal Timing

In its most basic form, traffic signal timing comprises determining the order of operations and allocating green time to each approach at a junction while also accounting for the time required for pedestrians and other users. To understand signal timing, we must first analyze numerous key topics: cycle lengths, splits, peak hour trends, phases, pre-timed and actuated signals, optimization, coordination, and communication.

Traffic Signal Timing 

Here’s a quick primer on traffic signal timing so you can better comprehend the practicalities of your everyday commute.

Cycle Duration

A cycle length must show all junction phases indicated by traffic loads and operate well within a set range. Signal timing tries to enhance efficiency by shortening cycle length. Cycles can last anywhere from one to three minutes. This is decided by a split. The split includes both the green period and the clearance interval, as well as the yellow and red lights. Clearance interval timings are calculated using perception or start-up time as well as acceleration rates. When switching signal phases, clearance intervals are usually referred to as change intervals. Because no cars pass through the intersection, the time between vehicles stopping or starting is known as “lost time.”

Pre Timed and Actuated

Pre-timed signal timings are pre-determined based on observed traffic volumes and trends and do not change based on traffic loads. This is especially true in city grid settings with near crossings and one-way streets, where maintaining inductance detection loops for each signal point is impracticable. Signal timings can be semi-actuated or fully actuated. Semi-actuated timings only detect minor streets, whereas fully-actuated timings detect all approaches. 


If you come to a stop at a red light on a minor road near a major intersection, the signal will change to enable you to proceed. Pre-timed signals have preset timing plans that vary during the day, whereas fully-actuated signals have a range of green times that vary based on actual traffic on the road. Customizable signal timing plans can be developed in the signal controller. These signal timing techniques must be fine-tuned.


Signal timing is performed at isolated and system intersections. As the name suggests, Isolated crossings are separated from other signalized intersections, and their signal timings do not affect other intersections. Because system intersections are close together, any timing changes at one affect the upstream and downstream intersections. Signal system corridors are frequently organized by peak period. These are the most common peak times. Traffic patterns or daily commutes usually determine these peak times. Traffic patterns cause peaks in the morning and evening. During the day, traffic patterns are frequently balanced.


To activate traffic lights, sensor systems must first detect an oncoming vehicle. Radar, sub-pavement electromagnetic pucks, and video detection are a few examples. Inductance loops are wires that run from the traffic signal cabinet to saw cuts in the pavement. It detects a vehicle over the loop saw cut region, commonly at the side street and mainline left approaches. Radar and video detection are less intrusive and require less maintenance. However, standard saw-cut inductance loops have proven to be the most reliable detection approach when properly maintained by Fairway Electrical voltage testing services


The “brains” of the traffic signal are housed within the traffic signal cabinet. The controller tells the signal what to do, when to do it, and for how long. The controller receives input from the detection system, decides how to respond, and then instructs the traffic lights.

Traffic Management Centers

Signal system corridors can be remotely monitored and controlled using fiber optics, copper wiring, or wireless networks in many circumstances. The same software that runs the traffic signal controller locally can be executed on the computer desktop of a traffic management center. The computer can interface directly with intersections and modify traffic signals that are operating remotely. During unusual occurrences or incidents, authorities can adjust traffic plans or patterns remotely and identify systems that are in need of traffic light maintenance


Because many variables, such as local trends and driving habits, cannot be measured by science or engineering, signal timing is sometimes referred to as an art. So, the next time you’re driving through green lights, take a moment to reflect on the complications that led to that great traffic scene.