Variations in traffic light operation

A single four-way flashing light showing only one color in each direction may be used at intersections where full three-color operation is not needed, but stop or yield signs alone have not had acceptable safety performance.

Yellow lights are displayed to the main road, to highlight the intersection and inform drivers of the need for caution.

In the United States, the flashing yellow arrow is not allowed where left turns and other traffic share the same lane.

British Columbia has adopted a non-standard meaning for a flashing green light, using it to indicate that the signal is controlled by pedestrians (and occasionally bikes).

[13] In Austria,[14] Croatia[15] and Estonia[16] a flashing green light gives advance notice of a change to amber.

In Regina, Saskatchewan, left-turn signals are designated by a two-bulb light configuration with one (or two) red balls and one LED bimodal arrow.

[17][better source needed] When a left-turn cycle begins the red ball will change to a flashing green arrow to permitted all traffic turning left.

Layouts are typically simple: either the usual three-disc all-directions signal; the same with a separate green left or right filter arrow which lights up either independently of the main green (permitting a turn in the indicated direction at an otherwise red light) or along with it (showing that conflicting traffic has been stopped so turning traffic does not need to yield, also known as give way in the UK); or using adjacent sets where the horizontal positioning and lane layout (particularly where lanes are segregated by kerbs or islands) denotes which directions are stopped or free to move.

This allows permissive turning even when straight-through traffic is shown a red light, avoiding yellow trap.

Louvers are fitted over the green and yellow balls of the left turn signal head to prevent driver confusion.

The 2009 Manual of Uniform Traffic Control Devices prohibits this display for new installations in favor of the flashing-yellow-arrow left-turn signal, which accommodates both permissive and protected left turns.

The signal was accompanied by a sign stating that left turns (against oncoming traffic) were required to yield on a green ball.

This function is not enabled at intersections where it may not be safe to do so (restricted view of oncoming traffic, heavy pedestrian crossings, or double-lane left turns are good examples).

Delaware and Maryland have also been known to place flashing red arrows at certain intersections, especially when no signal is needed for cross traffic.

However, this was allowed only when an engineering study determined that a "stop condition" must be imposed during the permissive left turn movement.

After the pedestrian pushes the button to trigger the signal, the light becomes a steady green until the sequence of yellow, then red (at which time the pedestrian crossing gives a walk signal) as in a conventional set of traffic lights, then returns to flashing green until another crossing is requested.

Current users of flashing green signal are Austria, Belgium, Estonia, Finland, Great Britain, Hungary, Netherlands, Norway, Mexico, Poland, Russia, Spain and Sweden.

This phase indicates that a public transit vehicle – bus, streetcar, or LRT – may proceed through an intersection in any direction while all other traffic faces a red light.

[30] The horizontal bar is generally considered the "red" phase and symbolizes traffic flowing across the intersection from the perspective of the tram.

The colors of these secondary lighting devices vary regionally depending upon the operational policies of the local traffic management and emergency service agencies.

[32] Some jurisdictions use special small blue lights on the back sides of signal heads to indicate red -light state.

In Austria, Cambodia, China, Croatia, Estonia, Latvia, Lithuania, Montenegro, Russia, most of Israel, Malaysia, most of Mexico, some places in Thailand, Turkey, Saudi Arabia, parts of Serbia, and in certain other parts[further explanation needed] of Europe, the green lights will start flashing at the end of the Go or Turn phase to indicate that the yellow (Caution phase) lights are about to be engaged.

In most European countries (including Austria, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, the Czech Republic, Denmark, Estonia, Finland, Germany, Hungary, Iceland, Latvia, Lithuania, Malta, Moldova, Montenegro, North Macedonia, Norway, Poland, most of Russia, Serbia, Slovakia, Slovenia, Sweden, Switzerland, Ukraine, and the UK), as well as in Argentina, Bahrain, Botswana, Colombia, Hong Kong, India, some places in Indonesia, Israel, Liberia, Macau, Pakistan, Paraguay, and the United Arab Emirates, red and yellow lights are displayed together for one, two, or three seconds at the end of the red cycle to indicate that the light is about to change to green.

These are relatively common in areas such as the United States, Canada, Western Australia, New South Wales,[35] New Zealand and Liberia.

The Canadian provinces of Quebec, New Brunswick, and Prince Edward Island generally use horizontal traffic lights with red to the left and green to the right.

It serves the same purpose as the vertical Texan configuration, and mainly appears on boulevards with multiple lanes of traffic where a left turn is dangerous due to poor visibility.

These so-called "Heuer-Ampeln", developed by the German Heuer-Hammer company were used in the Netherlands, Austria (Vienna) and Germany from the 1930s until the 1960s, with the last of them being replaced with the by then common known traffic lights in 1972.

A full, uninterrupted yellow bar will appear for a few seconds before, after a short blink, lights turn red.

This corresponds to the usual position of a red light (leftmost, or rightmost if at the other end of the road and at the other side of the pavement; or the upper third).

Some metered ramps have bypass lanes for high-occupancy vehicles, allowing car-poolers and buses to skip the queue and get directly on the highway.