Unusual uses of traffic lights

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Swedish traffic light (left) for use by public transport vehicles only. All signals use white lighting and special symbols ("S", "–" and an arrow) to distinguish them from regular signals. The small light at the top tells the driver when the vehicle's transponder signal is received by the traffic light.

Unusual uses of traffic lights, as used in various regional locations, may for example include traffic lights used in a non-standard fashion, or in a non-standard arrangement, or for specific traffic.

[edit] Unusual traffic light phases

[edit] Turn indications

[edit] Turn prohibition

In Winnipeg, Manitoba, Canada some of the signals have a special phase where there is a red light illuminated simultaneously with a green straight arrow. The meaning of this configuration is that a motorist may proceed straight, but is restricted from turning both left and right. An example of this is at Nairn Avenue and Archibald Street. Many of these signals have been replaced in recent years with standard protected or permissive signals that are more familiar to visitors during the course of signal modernization. Also, there is a traffic light on McPhillips Street and Kingsbury Avenue that has a U-turn signal on it as the crossing road is constructed with a barrier to block a legal left turn. In the Province of Quebec, a similar function is also in use where a green straight arrow is displayed alone, usually for 5 to 9 seconds and then the full green (or right turn arrow) illuminates. This allows pedestrians to engage into the roadway, and therefore (in theory) increases safety. Soldier's Field Road in Brighton, Massachusetts at the intersection with Nonantum Road, Birmingham Parkway and North Beacon Streets always has a red ball. Green arrows appear with the red ball to allow traffic to travel in a particular direction, but the red ball always is illuminated. The same is true at the intersection of Cambridge Street and Massachusetts Avenue near Harvard Square in Cambridge, Massachusetts, and at the intersection of West 3rd Street and Mesaba Avenue in Duluth, Minnesota.

[edit] Indication of protected turn

In parts of Canada (the Maritime Provinces, Quebec, Ontario, Saskatchewan and Alberta), a flashing green light has a special meaning. It is only shown in one direction, with the other three directions in a 4-way intersection having a red light. It gives the traffic in its direction the right of way in all directions; straight through, left turn or right turn. The light phase is known as "advanced green", and a sign saying "Advanced green when flashing" is usually attached to the light in question. The opposite side often has a sign attached to their lights saying "Delayed Green Wait for signal" or "Opposing Traffic Has Advanced Green." Advanced green indicates that the opposing traffic is facing a red light, and it is safe for the driver to turn left. In Ontario, older lights with this system are slowly being phased out in favour of more universally-understood left-turn arrow signals. In Alberta and Saskatchewan as a legacy, left-turn arrow signals also flash, rather than being displayed steadily as is done elsewhere.

Protected flashing green is now used in parts of California^[1] and Ontario as part of traffic signal preemption for emergency vehicles.

At certain intersections in Alberta (and possibly other places permitting a right turn to be made during a solid red light, also known as "right turn on red"), a solid green right-turn arrow will illuminate underneath a solid red light to indicate that traffic coming from the right side of the intersection has a protected left turn (blocking traffic coming from the left side) and thus a right turn can be safely made.

[edit] Indication of permissive turn

[edit] Flashing yellow arrow

In Oregon (and elsewhere in the United States) signals with a flashing yellow arrow are being phased in to replace the 5-lamp protected/permissive signals in widespread use. Three models of this signal have been seen in Oregon; one with 4 lamps — a (solid) red arrow, a (solid) yellow arrow, a (flashing) yellow arrow, and a (solid) green arrow; and two with 3 lamps. One signal has a solid red arrow, a solid yellow arrow, and a third lamp which can either be a solid green or a flashing yellow arrow. The other 3-lamp signal has a (solid) red arrow, a (solid) yellow arrow and a (flashing) yellow arrow (same yellow lamp), and a (solid) green arrow;. The solid arrows all have their usual meanings; a flashing yellow arrow indicates a "permitted" left turn (drivers may turn left without stopping, but opposing traffic has the right-of-way).

A pole-mounted flashing left turn signal in Oregon.

Unlike the five-lamp protected/permissive signals, the 3/4 lamp signal with flashing yellow arrow has one unusual configuration; if traffic in one direction has a protected left turn (green arrow) along with a green light for traffic heading straight — the signals in the opposite direction can (and do) show a red light for traffic going straight, but a flashing yellow for traffic turning left. Thus the traffic facing a green light has fully protected left turns (oncoming traffic is stopped) but straight-through traffic is not fully protected — left turns across its path from the opposite direction may be legal. However, the straight-through traffic does have the right-of-way.

[edit] Green ball, when main light is red - Dallas phasing

In the Dallas/Fort Worth Metroplex, the five-light permissive left turn light is often used in a different manner than standard signals of this type. When the light is red, but oncoming traffic has a green light and a green arrow showing, the normal green light will show on the 5-light bar; this signals that left turns are allowed out of the left turn lane if no other traffic is coming. If the light turns yellow for the oncoming traffic, so does the one on the 5-light bar; if the arrow expires, the light on the 5-light bar stays green, and all other lights turn green as well. For permissive signals that are used in this manner, black screens are fitted over the normal green and yellow lights, and the entire 5-light bar is turned at a slight angle. This arrangement prevents drivers in other lanes from thinking they have a green light when it is in fact red. Usually, such signals are accompanied by a sign that says "Left turn YIELD on green" with a green ball underneath the text; however, these signs have also appeared next to a normally functioning permissive signal in other Texas cities.

[edit] Flashing red ball or arrow

In Michigan, a flashing red ball signal on a "protected" left turn traffic signal indicates that left turning traffic may, after a full stop, complete their turn if and only if there is a long enough break in oncoming traffic. The flashing red usually occurs when the oncoming traffic has a green signal. 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). Michigan usually indicates signals that are dedicated to turning traffic with a sign displaying "LEFT" or "RIGHT". This sign is normally illuminated at night. More recent installations in Michigan, however, have used flashing yellow arrow signalheads, which typically have not included left-turn signal signage. All flashing red ball signals will gradually be replaced, because the flashing yellow arrow signals will become a U.S. standard.^[2]

Maryland and Delaware have also been known to place flashing red arrows at certain intersections, especially when no signal is needed for cross traffic. The driver is supposed to come to a complete stop before making his turn. This has been published in the 2009 MUTCD as an alternative to the flashing yellow arrow.

[edit] Crosswalks

[edit] Flashing green light

In British Columbia and and a few U.S. states, a flashing green signal is used at a pedestrian crossing, at which pedestrians have the ability to stop traffic to allow a safe crossing. They may also be used at a drawbridge. The flashing green indicates that the signal is not currently in use. As soon as a pedestrian pushes the button to trigger the signal, the light changes to solid green for a short time before entering the normal yellow/red/green sequence, then returns to flashing green until another crossing is requested; however, in some places such as Vancouver, it goes directly from flashing green to yellow, leaving out the solid green sequence. In Massachusetts, specifically in Cambridge and Somerville, the main street will have a flashing green signal, while cross streets have a signal that have a red on top, yellow in the middle and flashing red in the bottom position. When a pedestrian activates the signal, the cross street changes from flashing red in the lowest position to yellow to red (topmost position).

In Ontario, Quebec, New Brunswick and Nova Scotia, a flashing green light for indicates that the opposing direction still has a red light, thus drivers are free to make a left turn.

In several European countries, a flashing green light is used in crosswalks to indicate that signal is going to change from green to red soon. Therefore, flashing green has roughly the same meaning to pedestrians as ordinary yellow signal has for motorists. Slow-moving pedestrians are warned about oncoming signal change and have opportunity to wait for next signal cycle. Motorists are more likely to notice flashing signal. Drivers of vehicles about to cross pedestrian crossings should be more aware of incoming pedestrians.

Current users of flashing green signal are Austria, Belgium, Estonia, Finland, Great Britain, Hungary, Netherlands, Norway, Poland, Spain and Sweden. France, Portugal and Switzerland make limited use of flashing green.

[edit] Flashing red lights

In Australia, a flashing red pedestrian light is used at between green and steady red; it means "complete crossing but do not start to cross". This has a similar meaning to European flashing green, but means that if a pedestrian glances at it, they will not enter an intersection without enough time to leave.

[edit] Red and yellow light

In Massachusetts only, a red and yellow light on at the same time indicates that people may be crossing in the crosswalk.^[3] This replaces the extra "WALK/DONT WALK" signal. (Note that the MUTCD forbids this, in Section 4D.08, "Prohibited Steady Signal Indications".)

[edit] Other

Traffic lights for pedestrians are usually different; see pedestrian crossing. Traffic lights at level railroad crossings are again different. Both of these are to avoid confusion as to whom the signal applies.

[edit] Special signals

[edit] Transit priority signal

In Oregon, Ontario, Quebec, British Columbia, Nova Scotia and Manitoba, traffic signals may also have an extra white rectangular light mounted above the red light. This phase indicates that a public transit vehicle may proceed through an intersection in any direction while all other traffic faces a red light.

In some areas such as Boston, Massachusetts, a trolley may have its own traffic signals, indicating that it is okay for it to cross an intersection. These signals are all white, and the top section (stop) is a horizontal bar, the middle (caution) is an upright triangle, and the bottom (go) is a vertical bar^[4].

[edit] Emergency priority signal

In many locations in the United States, intersections use traffic signal preemption to give priority to emergency vehicles. These preemption applications often include an illuminated "notifier" signal. A notifier is a secondary lighting device usually mounted independently of the traffic signal, such as a standard or strobing light bulb in an omnidirectional enclosure or spotlights aimed at oncoming traffic lanes. The colors of these secondary lighting devices vary regionally depending upon the operational policies of the local traffic management and emergency service agencies.^[5]

[edit] Reverse side red light indicator

Some jurisdictions use special blue lights on the reverse of signal heads to indicate a red light lit on that head. They are used to communicate the presence of a red signal to police so they can view the situation without having to traverse the intersection.^[6]

[edit] Warnings that light will change

[edit] Change from green to amber

In Austria, Cambodia, Estonia, Latvia, most of Israel, parts of Mexico, Turkey, Russia, and in certain other parts of Europe, the green lights will start flashing at the end of the Go or Turn phase to indicate that the amber (Caution phase) lights are about to be engaged. This is useful in fast paced roads to allow for longer slowing down time, and for pedestrians crossing broad streets. Some traffic lights in Pennsylvania illuminate the amber light a few seconds before the green light turns off, to give this same warning. In Canada, flashing green lights will turn solid green before turning amber.

[edit] Change from red to green

In some European countries, particularly at urban intersections, at the end of the red cycle, the red and amber lights are displayed together for two or three seconds to indicate that the light is about to change to green. This phase aids drivers of cars with manual gearboxes and gives time for the driver to switch into first gear during the short phase, and release the handbrake.

[edit] Warnings of traffic light ahead

[edit] Flashing amber lights

In some areas, a "prepare to stop" sign with two alternately-flashing amber lights is installed in locations where a high-speed road (design speed usually at least 55 mph/90 km/h) leads up to a traffic light, where the traffic light is obscured from a distance (or both conditions), or before the first traffic signal after a long stretch of road with no signals. This is installed so that drivers can view it from a distance. This light begins blinking with enough time for the driver to see it and slow down before the intersection light turns yellow, then red. The flashing amber light can go out immediately when the light turns green, or it may continue for several seconds after the intersection light has turned green, as it usually takes a line of cars some time to accelerate to cruising speed from a red light. The City of Portland, Oregon used to use these on a regular basis but they have since become rare, the last new one having been installed on North Interstate Avenue in Portland in 2004. These are particularly common in the traffic jurisdiction of Western Australia at both railway level crossings, road intersections and truck routes.

One example of a preemptive traffic signal warning sign.

Another example of a warning sign.

[edit] Red Signal Ahead

In New Jersey, Pennsylvania, New York, Massachusetts, and Utah a common way of warning that an obscured traffic light ahead is red is a Red Signal Ahead sign. It is shaped like a standard yellow diamond shape sign with LEDs spelling out "Signal Ahead". Just before the traffic light goes yellow, the word "Red" will light up above Signal Ahead and they will begin to flash alternately.

In Perth, Australia a large sign is positioned a couple of hundred metres before the signals with alternating yellow signals when before the signals turn yellow. It is commonly used in high traffic intersections, especially on highways.

[edit] Strobed red lights

In some parts of the United States, a few traffic lights have slowly flashing white strobe lights superimposed on the center of the red light, which are activated when the red light itself is illuminated. These seem to be located in situations where the driver may have been travelling for a lengthy time without seeing any traffic lights (such as a controlled-access highway), in a place where a regular traveler wouldn't expect a signal (such as a newly erected signal or one put up for construction) or in other situations where extra work may be needed to draw attention to the status of the light (such as in an area where many other red lights approximate the brightness, placement and color of a red traffic signal). These are also used in areas prone to fog, as the strobing white light may be visible from a distance while the standard red light is not. A newer variant uses a flashing white LED ring located on the outer edge of the red indication as opposed to in the center of the red. Typically one strobe equipped signal is mounted as a supplement between two normal signal heads. It is worthy of note that such strobe installations have been prohibited by the FHWA since 1990; however, individual states have been slow to conform. The current MUTCD (2003 edition, revision 1) contain no provisions for their use; therefore, it is still FHWA's position that strobe lights are not allowed in traffic signals and no further experimentations with these types of strobe lights in traffic signals will be approved. This position was formalized on July 2, 2003 with an Official Interpretation of the MUTCD, number 4-263(I), "Strobes Florida DOT".^[7]

[edit] Unusual traffic light designs

[edit] Double red lights

A traffic signal in Halifax, Nova Scotia with specially-shaped lights to assist people with colour blindness.

The Canadian provinces of Quebec and Prince Edward Island generally use horizontal traffic lights with red to the left and green to the right. These signals also use specific shapes for each color, which aids color-blind people in distinguishing signal aspects:

• green — an ordinary "ball" shape,
• yellow — a diamond shape, and
• red — a square (somewhat larger than the ball shape).

In Quebec, most horizontal traffic lights have a red signal on both sides of the fixture (left and right). They are also now replacing the shaped traffic lights for blind people with regular round signals.

Some lights have two red lights, one on each end.

In Houston, Texas and surrounding areas, the use of a double red light is different. It is typically used on left turn signals. For horizontally mounted signals, typically hung or mounted over the lanes, it is configured with two red balls, one amber (yellow) arrow or ball, and a green arrow (from left to right). For vertically mounted signals, the two red balls are on the top, then an amber (yellow) arrow or ball, and a green arrow. It is usually accompanied by signs saying "left turn signal" or "left on arrow only." Signals for traffic going straight used standard signals, usually mounted horizontally over the road. The use of two red lights on the left turn signal allow for redundancy in case one of the red lights burn out, while saving money by requiring only one signal for left turns per direction that needs one.

One unique installation in Texas uses a double red light instead of a single red light to make the red light more pronounced and visible from a distance. In this unique installation, it is the first traffic light on a rural highway for miles, and traffic approaches at highway speed (65 mph). The double red light makes the red phase of the light visible at a farther distance than the yellow and green on the same signal.

[edit] Traffic lights in Tianjin, China

The "bar traffic light" in Tianjin (variant one)

The "multiple arrow traffic light" in Tianjin (variant two)

Tianjin in the People's Republic of China has two very special systems of traffic lights, in use since c. 1999/2000:

• One system is where there is a horizontal bar in a specific colour, with the colour changing and the bar shrinking. The shrinking bar indicates the time remaining in that colour. The colour itself is either red (stop), yellow or green (go). A blinking green one-third-full bar means "reduce speed now", and a blinking yellow full-bar indicates "proceed with caution".

When lights of this system turn from green to red, the diminishing green bar will flash once two-thirds (note: not the full bar) of the green bar is "eaten up", with the remaining third intact. A full, uninterrupted yellow bar will appear for a few seconds before, after a short blink, lights turn red. Immediately after the full red bar appears, a tiny (almost unnoticeable) split/division appears to signify the bit that will not be "eaten up". 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). When two-thirds of the red bit is "eaten up", the red light extinguishes, only to be replaced nearly immediately with a full chunk of green (again with the minute division). The process then repeats itself.

• Another system is where there is a set of three lights as traffic lights, but every light is an arrow pointing in different directions and every arrow has a colour of its own, to show whether traffic flow is permitted or prohibited in that direction.

The major disadvantage of this system of traffic light is that it is unfamiliar to those who are used to seeing specific colours of the traffic lights at the various ends of a normal traffic light itself (e.g. green rightmost, red leftmost, etc) as well is being problematic for the color blind. It does, however, conserve space.

Elsewhere in China, a blinking green light means "reduce speed now", attempting to stop cars from passing (if that car can still safely stop in time) and is nearly universal in appearance. Some cities or parts of cities show the number of seconds remaining in a specific traffic light colour (a so-called "countdown meter").

Another type of signal that can be found in China is the Unilight signal that displays all three colours in one signal section.

[edit] Unusual uses of traffic lights

[edit] Ramp metering

Main article: Ramp meter

A ramp meter or metering light is a device, usually a basic traffic light or a two-phase (red and green, no yellow) light, that regulates the flow of traffic entering freeways according to current traffic conditions. They are intended to reduce congestion on the freeway in two ways. One is to ensure that the total flow entering the freeway does not exceed the capacity at a downstream bottleneck. A second is to break up platoons of vehicles entering freeways, ensuring that traffic can merge more easily. Some metered ramps have bypass lanes for high-occupancy vehicles, allowing carpoolers and buses to skip the queue and get directly on the highway. Meters often only operate in rush hour periods.

On some large toll bridges, such as the San Francisco-Oakland Bay Bridge, red/green traffic lights, similar to ramp meters, are used to stagger traffic leading into the bridge. In the Bay Bridge's case, approximately 25 lanes of toll booth traffic are reduced to five lanes of bridge traffic in about 1/2 mile. To accomplish this, an overhead red/green traffic light is visible above each lane, several hundred feet beyond the toll plaza. Green is illuminated for 2 seconds, signalling the first driver in that lane to begin acceleration. Then the signal jumps to red for eight seconds. Using this method, there are always five lanes with a "green" signal, staggered throughout the 25 lanes of traffic.

[edit] Timers

Countdown to red light for vehicles, vice versa the digits are shown in red light (Sakon Nakhon, Thailand)

Countdown to red light for pedestrians (Nagoya, Japan)

Traffic lights are usually accompanied by timers that indicate how much longer a certain phase will last. This is especially common for pedestrian crossing lights in high-traffic areas. Timers have been extensively used in India.

In some cities (such as Kiev, Ukraine or Kraków, Poland) there are signs displaying how fast one has to drive in order to reach the next intersection at the exact time when the light turns green, thus allowing the driver to ease into a green wave.

[edit] Other

Other places where there may be traffic lights (normal or special ones):

• flashing signals used in conjunction with warning signs (such as dangerous curves, speed limit reductions, school zones, signal ahead, low clearance, flooding, iceing, or fog) and regulatory controls (such as Stop and Yield signs).
• on waterways with signs to implement special reduced speed "no wake" zones for watercraft.
• at public boat ramps to warn drivers before accidentally driving into the water.
• at the landing-stage of a ferry and aboard the ferry.
• at the entrance and exit of a parking place or garage.
• at the entrance and exit of some car washes, to indicate when the engine should be in gear and whether the brakes may be operated at a given time.
• at drive through lanes such as those at banks.
• at an international Port of Entry inspection station.
• at highway inspection and/or weigh stations.
• before a drawbridge.
• before a narrowing of the road.
• at a fire station or medical emergency entrance.
• at a tunnel entrance.
• in HOV Lanes.
• to allow cattle to cross — as on the A470 in Wales or A65 in North Yorkshire, England.
• at road construction sites to regulate temporary two-way traffic over a single open lane.
• at airports to regulate aircraft taxiways.
• adjacent to some airports where vehicular traffic on highways (crossing just past the end of a runway) must stop or yield during aircraft takeoffs and landings.
• at the entrance to water slides where they are used as a safety feature to prevent people going down slides too soon after each other.
• on automobile racing circuits to advise race drivers whether they can race or must slow or stop
• at the end of a dead end road to warn that the road ends, usually installed in locations where many accidents have occurred.

[edit] References

[edit] External links

• Left-turn Signal Display Animation Page from Evaluation of Traffic Signal Displays for Protected/Permitted Left-Turn Control (National Cooperative Highway Research Program report 3-54)

[edit] See also

• Traffic light