Editing Traffic light (section)

=== Timing ===
{{Main|Signal timing}}
[[File:Traffic_light_in_Tehran.jpg|thumb|A traffic light with a timer in [[Tehran]], Iran]]
The timing of the intergreen is usually based on the size of the intersection, which can range from two to five seconds.{{Citation needed|date=February 2023}} Modelling programs include the ability to calculate intergreen times automatically. Intergreen periods are determined by calculating the path distance for every conflict point in the junction, which is the distance travelled to the conflict point by the movement losing right of way minus the distance travelled to the same conflict point by the movement gaining right of way using the possible conflict points (including with pedestrians) and calculating both the time it would take the last vehicle to clear the furthest collision point and the first vehicle from the next stage to arrive at the conflict point. At actuated junctions, integreens can be varied to account for traffic conditions.<ref name=":1" />

Engineers also need to set the amber timings (and red–amber, where appropriate), which is normally standardised by a traffic authority. For example, in the UK, the amber time is fixed nationally at three seconds and the red–amber time at two seconds, which results in a minimum intergreen time of five seconds (plus any all-red time).<ref name=":1" /> The US also uses a minimum of three seconds, but local traffic authorities can make timings longer, especially on wider, suburban roads. This variation has resulted in controversy when municipalities with shorter amber times use red light cameras.<ref>{{Cite web |title=Yellow lights shorter in Chicago |url=https://www.chicagotribune.com/news/ct-xpm-2010-03-22-ct-met-yellow-light-20100322-story.html |access-date=4 February 2023 |website=Chicago Tribune|date=22 March 2010 }}</ref> Where pedestrian signals are used, the timing of the "inivitation to cross" – the period where a steady walk signal shows – and clearance periods – time when the walk signal flashes or no signal is shown – need to be calculated. This is normally set against a design speed, e.g. {{Convert|1.2|m/s|ft/s|abbr=on}}. Similarly, these can be made extendable using sensors, allowing slower-moving pedestrians more time to cross the street.<ref name=":1" />