Traffic light (from Latin ampulla , “small bottle [especially for ointments and oils]” , later transferred meaning “lamp”) is the colloquial term for a signaling device of a light signal system (LSA) or light signal system (LZA). The name also stands for the “traffic light system” as a whole. This is used to control road and rail traffic . Traffic lights order certain behavior for road users by emitting controlled signals. These traffic signs , which differ in shape and color , each have a different meaning and only work against the direction of travel of the traffic to be regulated.
In the traffic regulations of the German-speaking countries Germany, Austria and Switzerland, the traffic lights are designated differently. So it is as a traffic facility in Germany according Road Traffic Act (StVO) as a light signal system (LZA) referred. In the Austrian Road Traffic Act ( ) and in the Signalization Ordinance (SSV) to the Swiss Road Traffic Act , the designation light signal system (LSA) is used.of the
In the German StVO there is also a subdivision in green arrows . Usually only the first is referred to as a traffic light .according to alternating light signals , permanent light signals and
In technical regulations in Germany ( Guidelines for Traffic Signals (RiLSA) of the Research Society for Roads and Transportation ) and Switzerland (Swiss standards (SN) of the Swiss Association of Road and Transport Professionals ) is the term light signal system in use. In Austria (guidelines and regulations for the road system (RVS 05.04.3) of the research company road - rail - traffic ) the more precise designation " traffic light signal system" (VLSA) is used, but the designation LSA is among experts in Austria as well as in Germany and common in Switzerland.
The terms "traffic light system" or, for short, "traffic light" used in everyday language for a traffic light system go back to the similar pendant lights that were previously also known as traffic lights, more on this under Etymology . The first signal transmitters were suspended from wire ropes above the center of the intersection ( Heuerampel ) and were reminiscent of pendant lights. In the course of time, the word meaning as traffic lights came more and more to the fore. Especially when it is installed above the body of the road, you can still often find a hanging attachment, in some regions still swinging on wire ropes.
The colloquial term Ampel served as a source of other word creations in the German language. The terms traffic light coalition or the traffic light as food labeling can be traced back to the three traffic light colors.
Because of the variety of terms used in this article, the slang synonym traffic light is mostly used.
Only after the spread of electric light in the big cities were traffic lights again installed from 1912 onwards. The traffic light system installed on August 5, 1914 in Cleveland , USA , is considered the world's first electric traffic light and had only two lights, red and green. The first three-colored traffic lights found their way into Detroit and New York in 1920 . In Europe, the first three-color traffic light system - still mechanically controlled - was installed in Paris in 1922 ( Rue de Rivoli / Boulevard de Sébastopol ).
In Germany, the first traffic light system with the traffic tower at Potsdamer Platz in Berlin went into operation on December 15, 1924. On November 23, 1925, further systems followed at three intersections of Leipziger Strasse (Wilhelmstrasse, Mauerstrasse and Friedrichstrasse).
The first traffic light system in Hamburg was put into operation on November 14, 1925 at the intersection of Mönckebergstrasse and Glockengießerwall (identical to the intersection of Steintorwall / Steintorbrücke); it was developed by the Hamburg engineer Paul Arnheim . A few months later, others followed, including on Stephansplatz , whose traffic was previously regulated by six posts, each with two policemen.
There is no verifiable and plausible evidence for the statement mentioned in some places that the first traffic light in Germany was set up on Hamburg's Stephansplatz as early as 1922.
1925 was followed by Milan (Piazza Duomo) and Rome (Via del Tritone / Via Due Macelli), 1926 London ( Piccadilly Circus ) and Vienna (Opera junction), 1927 Munich (Station Square) and Prague (Hybernská / Dlážděná / Havlíčkova), 1928 Bremen (Brill ), Essen (Alfredstrasse / Bismarckstrasse) and Nuremberg (Königstor), 1929 Barcelona , 1930 Frankfurt am Main ( Kaiserstrasse / Neue Mainzer Strasse ), Leningrad , Moscow and Tokyo , 1931 Hanover ( Kröpcke ). Smaller cities such as Braunschweig and Krefeld (1951), Basel , Helsinki (1952), Lucerne (1952), Gelsenkirchen (1953), Heilbronn (1954) and Bremerhaven (1957) received their first traffic lights in the 1950s.
Because road users only gradually got used to traffic lights and initially did not take their obligation seriously, there were inventions that underlined the visual signal with an acoustic signal, such as that of a London engineer:
“Outwardly, the speaking traffic light differs little from a normal system. [...] In a housing connected to the lamp box there is a very compactly constructed small magnetophone device with a tape that serves as a carrier for traffic commands, or better warnings, which are announced in a pleasant male or female voice through a built-in loudspeaker. "
Etymology of the word traffic light
The term traffic light is a borrowing from Latin ampulla (actually * amp (h) orula , then * amporla , * ampurla ), piston-shaped vessel with two handles', 'small bottle' (see vial and bottle ), a diminutive of Latin amphora ' Two-handled clay vessel' (with a subsidiary form ampora ), which itself is borrowed from the synonymous Greek ἀμφορεύς amphorēūs . Ampel - Old High German amp (ul) la , Middle High German ampulle, ampel , Middle Low German ap (p) olle, appulle - was initially referred to as a "small vessel for oil or other liquids", mostly intended for consecrated use, especially the eternal one in the Middle Ages Lamp in the church (a constantly burning oil lamp hanging from the ceiling), from the 14th century to the light source in the house (since the 16th century it has been in competition with lamps ).
Traffic lights, the abbreviation for traffic lights, are being revitalized in the 20th century.
There are various reasons for using traffic lights, for example to regulate the flow of traffic and to prevent dangerous or dangerous traffic situations ( traffic safety ). In road traffic these are intersections and junctions as well as bottlenecks, for example at construction sites or bridges.
Crossings and junctions
Traffic lights are used at intersections or junctions (intersections) for the following reasons:
- The system can serve to optimize the flow of traffic. With high traffic densities, for example with several lanes in each direction, traffic lights allow the best control of the traffic flow.
- They can help defuse dangers at complicated or confusing intersections. At junctions with more than four directions, the regulation with traffic signs can be unclear or confusing and lead to accidents. A traffic light system simplifies such situations with clear instructions, possibly supplemented by additional warning lights, for example if oncoming traffic has to be given priority.
- They can be used at intersections with a corresponding volume of traffic, where no roundabout can be set up for reasons of space .
To pedestrians to enable safe crossing busy roads on roads, pedestrian signal system (also called "pedestrian protection systems") are used. These systems are often operated with a request (almost always at the push of a button) by the pedestrians. Variants are possible in which the signaling devices for vehicle traffic are switched to "dark" in the basic position. When requested by the pedestrian, the vehicle signals switch from dark to yellow to red.
Pedestrian signal systems usually serve as a crossing aid on (floor-marked) pedestrian protection paths, the zebra crossings. With sufficiently slow vehicle traffic, which can be promoted by the traffic organization (see Shared Space ), and alternate consideration by waiting for pedestrians on the one hand and opening gaps in a column of rolling vehicles, eye contact and communication on the other, pedestrians can cross flexibly and safely in terms of time and space. Pedestrian protection path and signal system organize crossing (including children's cycling, skating, pushing bicycles, wheelchair use) locally in one place (and forbidding it up to 20 m away) and in time slots. With high pedestrian traffic and limited sensors and logic of the traffic light system, pedestrian traffic lights quickly reach their limits. It is not uncommon for pedestrians to be injured on protective routes by vehicles crossing incorrectly.
If there is bicycle traffic on the road, the same signals apply to bicycles and vehicles. The problem with traffic lights in many places is that induction loops in the road are so insensitive that they do not recognize bicycles.
Where cycling takes place on cycle paths, cyclists often have to follow the pedestrian traffic lights, which are then equipped with so-called combination signals, i.e. the signal color is emitted in the form of a pedestrian and a bicycle symbol. Since cyclists need much less time to cross a lane than pedestrians need, separate bicycle signals enable much longer green phases for bicycle traffic. In some places these are small signaling devices at the waiting position for bicycles. Elsewhere, the bicycle traffic light is placed across the intersection. If the bicycle and pedestrian ford are right next to each other, there is then the possibility that visually impaired pedestrians hold the bicycle signal for the pedestrian signal and step onto the lane too late.
All around green
In some places you can find a so-called all-round green at intersections, which means that crossing bicycle traffic is given the green light at the same time. This can make it easier to turn left, but ultimately means longer waiting times for all types of traffic. There is also an increased risk of accidents between cyclists, especially towards the end of their green phase. In the Netherlands there are therefore warning signs at intersections with all-round green.
In Germany and some other countries, when the traffic light is red, you can turn from a cycle path to a cycle path at a crossroads, provided there is no lane to cross and there is no stop line in front of the pedestrian ford on the cycle path. In the Netherlands, such a turn is only allowed in places with an additional sign.
Public buses and trams
In streets with bus lanes, there are special signals for public buses in some countries, similar to trams. They glow white and work with shape symbols instead of color symbols.
Light signal systems are also used to control bottlenecks, for example on construction sites. Temporary mobile systems (construction site traffic lights) are usually set up. These systems usually only have two signal transmitters. They regulate a single-lane road section that can only be driven in one direction ( one-way traffic) . It is important to set the clearing times correctly, which vary depending on the length of the bottleneck. Since these systems are mostly used on the move , they are equipped with rechargeable batteries or a photovoltaic panel as power supply and with a radio link.
Light signals can be used to completely block a road section, for example to block the entrance to a tunnel in the event of a traffic accident or fire. The associated signals are normally dark and change from yellow to red when blocked.
Traffic lights can be used on private property to regulate access (underground car park entrances with only one lane or car washes). Since you usually only drive at walking pace here , you often limit yourself to the colors red and green.
Standard traffic light system
A normal European traffic light system controls traffic using the three signal colors red, yellow and green. These colors are displayed individually or in combination to regulate traffic. The sequence (called signal sequence or color image sequence ) of such a traffic light system is always:
- Red: No entry permit
- Yellow: waiting for the next signal
- Green: Traffic is clear
Red is the same throughout the world with the exception of the upside down Tipperary Hill traffic light in the city of Syracuse ( New York , USA). This enables people with red-green poor eyesight or color blindness to find their way around. For transverse traffic lights, the red light is on the left-hand side in countries with right-hand traffic, and on the right-hand side in countries with left-hand traffic, therefore always in the middle of the lane. In Switzerland, the green light used to be square and the yellow light triangular when the traffic lights were lying down. Today they have to be round.
The visual appearance usually consists of a black background with round or square light signals. To shield against sun light and prevent phantom light are screening diaphragms , and barges called mounted. If necessary, additional black / white contrasting panels are attached to the signal heads for better visibility .
Variants of the standard traffic light system in different countries
In individual countries, additional color combinations are possible at the same time or one behind the other:
- Red-yellow: Between red and green: Attention, permission to drive will be given shortly. For example in Germany, Great Britain , Croatia , Lithuania , Norway , Austria , Poland , Russia , Saudi Arabia , Sweden , Switzerland , Ukraine and Hungary . This phase lasts up to 2 seconds.
- Green yellow
- between green and red: attention, it will be red immediately (for example officially abolished in Italy in 1992, now extremely rare, also abolished in Sweden in 1999)
- between green and yellow: Attention, it will be yellow (for example in the GDR , not RiLSA- compliant, therefore gradually abolished after reunification )
- red flashing light: stop! Stop, then continue slowly when the intersection is clear. ( United States , Japan , South Africa , Taiwan )
- flashing green light
- At the end of the green phase: Attention, yellow will be shown in the People's Republic of China , Israel , Croatia, Lithuania, Latvia , Mexico , Austria, Russia, Serbia, Slovenia , Turkey and the Ukraine.
- At the beginning or at the end of the green phase: Protected left turns are possible in most Canadian provinces including Québec , but not British Columbia .
- instead of the green phase: Denotes a traffic light that only switches to red when pedestrians press the button (in British Columbia, Canada ).
- at the pedestrian traffic lights : Attention, it will be shown in red in Austria, Poland, Latvia, Lithuania, the Netherlands , Norway, Sweden, Japan, Singapore , Hungary and Romania , Switzerland (in certain cantons, e.g. Basel-Stadt ), Spain , partially to be found in Germany at cycle lane traffic lights.
- yellow flashing light
- Traffic lights out of order on the sides of the intersection that have to give way in Germany
- Traffic lights out of order, on all sides of the intersection, including those with priority, in Austria , Switzerland, Italy, Lithuania, Poland, and partly in Germany.
- instead of the green phase: Refers to a traffic light that only switches to red when pedestrians press the button (at some pedestrian crossings with traffic lights in Italy)
- after the end of the red phase, instead of red-yellow: continue only when there are no more pedestrians on the lane (at 'Pelican' pedestrian traffic lights in Great Britain , Cyprus )
- Crossroads can be passed carefully: United States (right of way in opposite directions with flashing red light), Japan
- yellow flashing light instead of green (in the lowest of the three signal fields) after the red phase: turning is possible while observing the right of way; Right of way conflict traffic possible (e.g. in France , Ireland , Switzerland)
- Green follows red instead of red-yellow: in Belgium , France, Italy, Spain, Portugal , Greece , Ireland, Japan, Luxembourg , the Netherlands, Romania, Australia , New Zealand , Taiwan , Brazil and the United States
- Red-green / green-red alternation without yellow phase: In the industrial centers of the People's Republic of China there are traffic lights that only change from red to green and vice versa. There are then no yellow signal fields. The systems have a counter which is counted down to zero in the respective color green or red. When zero is reached, a yellow signal field is only displayed from green to red, if available, and then switched to the other color after a short time. The countdown now starts again either immediately or for the last few seconds. Every pedestrian and vehicle driver can thus observe at any time how long the current phase will still be valid. Abrupt braking maneuvers are avoided and the waiting person is not stressed by uncertainty. There are a few such traffic lights in Germany, for example in Hamburg (in the streets around the Inner Alster). Alternatively, light bars are shortened in South Korea .
The meaning of the individual colors is not the same in all countries. For example, in the United States of America, Canada, and China, while red lights do not allow you to cross the intersection, most states and provinces allow right turns. In Germany there is a similar regulation with the additional green arrow sign next to the traffic light. If both the street you are exiting from and the one you are entering are a one-way street , many states in the USA are allowed to turn left, even if they are red, unless an additional sign prohibits this.
Traffic light woman (Zwickau)
In Europe, pedestrian traffic lights usually show the symbol of a standing (red) or walking (green) pedestrian ( traffic light man ). Yellow phases that follow the green phase can be found in Italy , Switzerland , Liechtenstein , Ireland and Düsseldorf . In the case of red, there are lenses with standing traffic light figures and in the case of green and yellow with walking men in the signal chamber. In Italy you can also see a standing traffic light man when yellow. The old, two-tone models (only red and green) - some with the inscription ALT for red and AVANTI for green and others with the conventional traffic light figures - are rare in Italy .
Instead, in some countries, a flashing green traffic light phase is displayed before the red phase. In Australia, a flashing red traffic light phase is shown before the red phase and the signal tone for the blind ends. Both phases order that pedestrians who are still on the lane quickly finish crossing the street and that the pedestrians should wait on the sidewalk.
In some cities in Germany there are three-field pedestrian signals. The signal chamber for red is available twice here. This enables people with red-green blindness to see at a glance whether the traffic light is red or green. It also prevents the system from being switched off for safety reasons if a red light fails.
There is a special feature of pedestrian traffic lights in Marl . Germany's first talking traffic lights were installed there in 2014 . This is a module that ensures that when the signal request device on the traffic light pole is operated, "Thank you, it will be green soon." With the pilot project, the city of Marl would like to offer visually impaired people further support and also encourage them to use the traffic lights more frequently and thus avoid “red light walkers”. So far, four plants have been equipped with the system, and more are to follow.
In Taiwan there are pedestrian lights with an animation of the green traffic light man. Towards the end of the green phase, the male changes from his previously leisurely gait to a more hasty running pace. In addition, the time remaining until the start of the red phase is displayed. There are also traffic lights in Tangier (Morocco), Turkey, Portugal and Spain with a traffic light man animated during the green phase.
|Polish traffic light men|
Pedestrian lights in North America have orange ( Portland orange ) and white ( Moon white ) signals . The ads appear either in text form (“Don't Walk” / “Walk”) or as pictograms (hand or silhouette). The signal sequence of a pedestrian traffic light is as follows:
- Hand: crossing prohibited;
- Silhouette: it is possible to cross the intersection;
- Flashing hand: End crossing (corresponds to the red phase in Germany before cross traffic is green). Often the number of seconds remaining for crossing the street is displayed in a countdown at the same time.
In many states in North America, text displays are no longer used with newer traffic lights. Here there is only the hand and the silhouette.
Procedure and technology
Rider traffic light in Essen
The lengths of the individual phases are specified in a signal schedule, or they are set depending on the traffic. In the time windows between the green phases of the different driving relationships , the critical traffic areas ( conflict areas ) must be cleared. These times are called intermediate times and are calculated according to the clearing paths, entry paths and speeds.
In the case of traffic-dependent control, the use of traffic detectors ( induction loops , motion detectors , video cameras ) extends the green phase so long that all vehicles in a group can pass. A maximum value is set in consideration of the reasonable waiting time of the other road users. A variable cycle time results from the sum of the traffic light phases. With fixed-time control, the green periods and the cycle time are constant over a certain period of time and are switched to other programs by automatic weekly switching. This enables a response to different traffic loads (work, day and night traffic, etc.). As a rule, the cycle time is between 45 and 120 seconds. As a rule, the longer the turnaround time, the higher the performance, but the longer the waiting times for road users. This increase in efficiency finds its limits when waiting left-turners jam back beyond their left-turn lane and clog the lanes. An individual algorithm is programmed for automatic traffic lights (so-called phase plan), these control, among other things, the phase transitions and, if necessary, requirements (e.g. public transport acceleration).
In large cities, the signal systems are usually controlled and monitored centrally. In this way , the appropriate programs are switched on for streets according to the time of day or the volume of traffic , disruptions are detected and traffic load data is collected.
With traffic-dependent control, the individual traffic flows are operated as required. The simplest form is the pedestrian traffic light with a push button (request). In the case of fully traffic-dependent systems, the length of the phases is calculated according to the size of the respective controlled traffic flows. With green waves this is only possible to a limited extent. The traffic-dependent control can be used to assign priorities to certain road users such as local public transport (ÖPNV).
Furthermore, fire brigades , the police or the military can intervene in the control. The fire brigades and the Federal Armed Forces can request long and prompt green phases for moving vehicles from the guards. Some systems also have a manual switch where the signal service or the police can influence the program sequence. There are the options normal operation , manual on (current state is retained), start (switching by one step), LZA off , LZA off and secondary direction yellow , all yellow and emergency stop . Program logics (also for manual control) protect the traffic from being released for all directions of travel (so-called “ hostile green ”).
At the intersections, several signal heads, which are interconnected to form a signal group, are attached for each direction. The signals are mounted on main lanes on whip masts, on short masts on the side of the direction of travel, for other parts of the road these are attached to the side or hang down. The installation is carried out worldwide predominantly in front of the protected area. In North America and South Africa, the signal heads are usually in the middle of the intersection. In Poland, the whip masts are sometimes a few meters behind the main right signal. So that the signal head can be seen by drivers standing directly at the intersection, smaller signal heads are sometimes installed at eye level.
Signal aspects are shown with single-colored diffusers (colored glass bodies with diffusing lenses in front of the lamps), certain driving directions (e.g. left-turning) are also shown with masks in various arrow shapes, called direction signals . Various forms of masks are also used for pedestrian, bus, tram or special signals.
In addition to the usual form of traffic lights, there are other types of traffic control:
- Green arrow inside the junction: This indicates that all traffic flows that are prone to conflict are red and the junction can be cleared; this is used as an auxiliary turn signal or additional right-turn signal for left and right turns.
- If the intersection is used by trams on an equal footing , there are usually additional signal heads with white illuminated fields. It means: horizontal bar = stop, vertical bar = straight ahead free, diagonally to the right or left rising bar = turn right or left free. White point = stop (corresponding to the yellow signal for motor vehicles). White triangle on top = permissive signal d. H. Driving permitted provided that priority vehicles are observed. These public transport signals can also be shown for buses on special lanes.
- At crossings directly at level crossings , the level crossing protection is integrated into a traffic light system. The security technology then becomes very complex. When the level crossing is closed, it gives preference to outgoing traffic. Such a plant is in Germany as BÜSTRA referred ( directives on dependencies between the technical safety of B ahn ü bergängen and traffic control on adjacent streets ßenkreuzungen and -einmündungen ).
In the case of large intersections, it is quite common to control the traffic within the intersection with additional light signals.
In addition to the traffic lights for general vehicle traffic, there are usually signs for pedestrian traffic and, in the case of bicycle traffic guides integrated in the intersection, for bicycle traffic. These only consist of a red and a green light. In some areas of Germany there are systems that consist of two red and one green lights for pedestrians and cyclists. The reason for this is that pedestrians and cyclists are better made aware of the waiting phase. In recent years, however, the second red signal has been omitted more often for cost reasons. The signals for pedestrians and cyclists can either be round like in Germany or rectangular like in Vienna. In most cases, a standing or a walking figure is symbolically displayed in the lens. For the cyclists only the symbol of a bicycle is displayed.
As a special feature in Dusseldorf coverage for pedestrians a caution period in the form of a horizontal beam, in contrast to the yellow signal of the traffic passing the clearance time is hereby signaled. In Aachen this special feature existed at two traffic lights until 2006, after many traffic lights were switched to light-emitting diodes , this was not adopted. In Düsseldorf, on the other hand, new traffic lights are again being equipped with the additional signal. The city is actively promoting the additional security with the title “yellow time” with posters and brochures. Pedestrian crossings with trams are often secured by two alternately flashing yellow lights (so-called auxiliary signals ), on which a tram is represented by a mask.
By connecting several systems one behind the other, which are coordinated with one another, a so-called “ green wave ” is possible with a constant cycle time . Competing planning issues in the design of a signal program are: green wave for motor vehicle traffic, green wave for bicycle traffic, continuous pedestrian crossing options across central islands, clearance time requirements or priority for public transport, traffic lights for the blind, safety aspects and performance.
In Germany one speaks of a gatekeeper system , gatekeeper traffic light , flow control or flow metering when the performance is deliberately reduced at a certain signal cross-section. It keeps the following section of the route free of traffic jams and thus functional. In addition, emissions from stationary and accelerating vehicles will be shifted to the area in front of the traffic light system.
Light signals on request and two-field signaling devices
In a demand traffic light (yellow and red, no green), with questionable-ended signal transmitters according RiLSA Chapter 1.4, incomplete in Austria Traffic light signaling equipment (UVLSA), usually in the basic position, no light signal is shown; There is no green. The general rules of right of way or the local signs apply as long as the traffic light is dark. Signals (yellow or red) are only shown when required. For example, the yellow light first lights up for five seconds and then the red light. After the end of the red phase, some systems still show the red-yellow phase known from systems with three lamps, others go out immediately after the red phase and allow you to drive off immediately, if no other signs prohibit this.
The purpose of a traffic light without a green light is to block a direction only when required on request. If the traffic light is dark (i.e. not green), this direction has no unrestricted travel (no priority), but must, if necessary, observe traffic signs and comply with the right of way, just as if there were no traffic lights. Such systems are often found at level crossings , pedestrian crossings , widened junctions and at the exits of emergency vehicles such as fire stations . The traffic lights without green light are also used at larger intersections , where they are switched on regularly (such as at Effnerplatz in Munich).
According toStVO (2.3), alternating light signs in Germany have "the color sequence green - yellow - red - red and yellow (simultaneously) - green". According to Section 2.3 (3), “traffic lights can be restricted to the color sequence yellow - red”.
Requirement traffic light system at a fire station ( Marl )
Traffic-dependent systems are used at intersections with weak cross-traffic, whereby cross-traffic is detected by traffic detectors only when a vehicle approaches ( induction loops or PIR sensors ) is released (release request). In the case of heavily loaded intersections, the release time can also be controlled by induction loops depending on the traffic.
If there is a need for pedestrian crossings, the traffic lights are only switched to green for a pedestrian at the push of a button (demand phase). Again and again there are pushbuttons at pedestrian crossings that supposedly turn the pedestrian traffic light to green, but are actually ineffective. For the waiting pedestrian they make use of the placebo effect on the waiting time. In some traffic lights, the next green phase does not actually differ whether the button is pressed or not, as it is possible at this phase of the signal flow plan and does not cause other road users to wait.
A special case is the “sleep light”, which only turns on when you press a button, thus saving energy. After being switched on (by a pedestrian pushing a button), this type of traffic light initially shows green for motor vehicle traffic, and then switches to red for motor vehicle traffic and green for pedestrians and back again. In the next green phase for drivers, it then switches itself off completely. The green light signal is often saved with such traffic lights, so there is only red and yellow light. If a pedestrian presses the request button, the yellow phase is switched on immediately for motor vehicle traffic, followed by the red phase. The traffic light is then switched off completely, which leads to a direct transition from the red to a (invisible) green phase.
Flow control systems regulate the flow of motor vehicles on motorways with the help of LZA.
If the installation of a vertical signaling device is not possible, for example due to a height restriction in a tunnel , these can be arranged horizontally, in the order red - yellow - green from left to right (applies to right-hand traffic). In Germany, horizontal traffic lights are not permitted according to the StVO.
The non-illuminated green arrow in Germany is a supplement to traffic lights, which shortens the waiting time for turning right in certain traffic situations. It is represented by an arrow pointing to the right on a small sheet of metal to the right of the red light of the traffic light (sign 720). It allows vehicles to turn right despite the red light at a traffic light if they have stopped at the stop line beforehand and if there is no obstruction or danger to other road users, especially pedestrians and vehicles in the direction of traffic allowed.
In some places, cyclists are offered a traffic light handle to hold on to.
Additional information for road users
Acoustic release signals
Many pedestrian traffic lights are also equipped with acoustic release signals, by means of which the visually impaired can recognize from the noise whether they are allowed to walk or not and in which direction the release is taking place. The acoustic release signal must have a frequency of 880 Hz ± 50 Hz and should be operated with a clock frequency of 2 Hz ± 10%. The on / off ratio is 1: 1 ± 10%. In order to be able to find the signal mast, pilot tones are often given to the signal mast. They need to be clearly different from the release tones. The RiLSA propose a ticker noise in continuous operation, which should be heard within five meters of the signal mast. Another possibility are tactile signal transmitters (mostly yellow boxes), on the top of which a vibration plate with a tactile arrow is attached. When it is green, this plate vibrates.
For the visually impaired, the crossing situation is shown in a symbolic relief on the sides of some button pushers. The relief gives the visually impaired an overview of the crossing.
The relief reads from bottom to top. It consists of different modules that are put together depending on the transition. Each transition begins with the start symbol, consisting of an arrow and a broad line that represents the curb. This is followed by various other modules for traffic lanes and islands. The relief is completed with a broad line.
Modules for traffic lanes consist of a line in the middle and a symbol for the type of traffic to the right or left of the line, depending on the direction from which the traffic is crossing the transition. If it is possible to cross from both directions, the symbol is on the right as well as on the left. If the transition is secured with a traffic light, the middle line is solid, otherwise it is dashed.
A bike path is represented by two horizontally adjacent points, a vehicle lane by a rectangle and tram tracks by two lines lying one above the other.
Islands are represented as a rectangle with semicircles on the right and left. If there is a request contact for pedestrians on the island, there is a point in the middle of the rectangle. If the island has access to a stop, the rectangle is open in the direction of the stop.
Remaining time display
Traffic light systems with remaining time display ( TTG - time to green ) show the remaining waiting time until the green signal in an additional field. Such systems exist both for motor vehicle traffic and for pedestrians and are the rule in some countries, but very rarely in Germany so far. In Augsburg, however, it has established itself for tram and regular bus services. In addition, there are traffic lights in many countries that show the remaining duration of the green phase, for example in Hamburg on the Inner Alster and at Bochum Central Station.
With traffic-dependent controlled traffic lights, the display of the remaining time is only possible with great effort and not always error-free.
Countdown of the clearance time
Light signal systems with a countdown of the clearing time show in an additional field at the beginning of the red phase of the pedestrians, with the help of decreasing bars, how much time remains to clear the lane until the green phase of the cross traffic. Such traffic lights are currently being tested in Berlin.
A speed signal ( GLOSA - green light optimized speed advisory ) is either a special light signal of a traffic light that is installed several hundred meters in front of the traffic light, or it is integrated in a smartphone app or in the on-board computer of a vehicle. The signal or the software recommends a certain speed to the vehicle driver so that he can pass an intersection during a green traffic light signal. The displayed speed is a recommendation , but not a speed limit . Future developments can make the need for traffic light control null and void if the individual road users communicate with one another and then be guided across the intersection at the optimum speed, if possible without stopping.
Signal systems for trains and buses
There are special forms for trams and buses (see tram signals in Germany ). These are interconnected with the standard traffic lights, but are only relevant for this means of transport. These signals (white symbols on a black background) apply to tram traffic nationwide in Germany (Appendix 4 of the BOStrab ), with the signals for trams and buses being adopted almost everywhere (in some places, however, there are other light signals for bus traffic). Signals with white dots, usually three horizontally and two vertically arranged, are called point signals in Switzerland.
With the help of a signal priority (also known as public transport prioritization ), selected types of transport can be given preference. It is usually used to minimize waiting times for buses, trams, the police or the fire department. Their approach is recognized with the help of special detectors ( infrared beacon system , overhead contact line ). The traffic light system then changes the length of the green time or the phase sequence in favor of these vehicles. The advantages are, on the one hand, a noticeable acceleration of public transport and the avoidance of accidents with emergency vehicles. On the other hand, it is advantageous for other traffic that special phases for buses and trams only need to be switched when such a vehicle is approaching the intersection.
However, it is hardly possible to maintain a green wave with public transport prioritization.
Traffic light control
The planned influencing of the traffic flow by means of light signals is referred to as traffic light control. The so-called deployment point control is used for this, for example . This is a light signal control in which the signaling states are switched via defined points of use . The fixed-time signal control can also be used. In this case, the road user cannot influence the traffic light control (for example through a demand phase).
A basic distinction must be made between individual control and group control . With the individual control, the traffic flow is controlled with a traffic light system without coordination with other traffic light systems. With group control, on the other hand, coordination is set up between several traffic lights. A group node is a node in a group at which the traffic signal systems are connected to one another for control purposes.
Influencing traffic light phases through adaptive traffic control
In the early days of traffic engineering, adaptive traffic control could only access induction loops in the road surface and the pedestrian pushers and thus react to the volume of traffic and people.
Modern signal systems adapt to the following influencing factors:
- Cameras or motion detectors detect the movement and the need to cross vehicles, bicycles or pedestrians.
- Cyclists recognize ground loops on cycle paths.
- Smartphone apps register cyclists at traffic lights or specify the optimal speed for a green cycle wave.
- If more vehicles are driving in a green phase than usual, this can allow more vehicles to pass by extending the green phase . The green phase extension is also used if the traffic light would actually switch to red according to the program, but a vehicle was still recognized as a latecomer. The green phase extension is used to increase road safety when two vehicles are in the dilemma zone and there is a risk of a rear-end collision if one vehicle brakes in yellow, but a subsequent vehicle does not notice the braking and accelerates at the same time in order to still be in last moment to pass the intersection.
- Local public transport (ÖPNV) can be preferred automatically or on request .
- Emergency vehicles from the police, fire brigade and rescue services are accelerated centrally, on the one hand, by the control center influencing the traffic light switching along the planned route ( preemption mode ), on the other hand there is also the option of using coded light transmitters on the emergency vehicles and receivers at the traffic lights unlock the path within sight.
- With increasing levels of pollutants, cities and municipalities also attach importance to emission-related traffic control.
Special types of control
A special form of traffic light switching is the diagonal crossing (all-round green) for pedestrians. All pedestrian signals at an intersection show "green" at the same time, which allows any crossing of the intersection. Turning accidents between vehicles and pedestrians are avoided, but the average waiting time for all road users increases. This regulation, which is very common in Japan, is rarely used in Europe. In some places it is used for bicycle traffic, with the risk of accidents between cyclists.
Another special type that is very common in Switzerland, for example, is the “ Everything red - immediately green” circuit. In the rest position, the traffic light system shows “red” on all signal heads. The green phase can be requested via detectors located at a distance (e.g. at a permissible speed of 50 km / h at a distance of 65 m from the stop line) or request devices for pedestrians attached to the masts. The switchover usually takes place immediately, since after longer red periods there is no longer any need to wait for intermediate times. Approaching vehicles can pass the junction without delay, but faster vehicles (over 50 km / h) have to reduce their speed.
If the control of a traffic light system fails or a malfunction occurs, an emergency signal program or a substitute signal program is started automatically and the signals of the "secondary directions" receive a yellow flashing light. If the red lights of a "main vehicle signal" fail, a red fail-safe device is installed and the system also switches to flashing yellow.
A self-sufficient signal protection ensures that two crossing directions do not have green (" hostile green ") at the same time due to any switching or component errors . In this case, it also switches to flashing yellow.
The yellow flashing light indicates a dangerous situation where you have to give right of way, and there must always be right-of-way traffic signs at crossings and junctions with traffic lights for a possible failure of the system. The other traffic rules apply accordingly to crossings and junctions without traffic lights.
At intersections that are not very busy at night, the traffic light systems are often switched off after a certain time, so that - analogous to the failure of a system described above - only yellow flashing light is shown. The signal heads are dark on the road with right of way. The risk of serious accidents would then increase by around 25%, and the economic damage would be significantly higher than the electricity costs saved by the municipality. Among other things, the accident research of the insurance companies (UDV) therefore considers switching off the traffic lights to be unacceptable for reasons of traffic safety. In 2011, the State Office for Roads in North Rhine-Westphalia calculated that switching off an intersection saves around 330 euros per year and switching off pedestrian traffic lights around 155 euros. When traffic lights are switched to LED lights, the power-saving effect becomes much less important.
Behavior in the protected area of a traffic light system
Traffic lights showing red light have priority over other traffic signs and are not allowed to be passed, unless instructed otherwise by a traffic control. In Germany there are still the exception to the panel Green Arrow , where you also can turn to stop at red lights. A vehicle must normally be stopped in front of the stop lines. A red light violation has already occurred when the vehicle driver enters the so-called protected area. At intersections monitored by cameras, a control recording is always made, as the vehicle driver could have driven back again.
If it is red, you must stop before the first stop line. At junctions shortly before the traffic lights, at property exits or at taxi stands, there may be two stop lines. The first stop line is mandatory for regular traffic, whereas the second stop line, behind the first and therefore closer to the traffic lights, is mandatory for special traffic. If regular traffic does not stop at the first stop line when there is a red light , there is a red light violation according to established case law .
If you bring the vehicle to a stop too far in front of the stop line, you may not be registered by the induction loops laid in the roadway . In the case of traffic-dependent LZA, the green of your own direction of travel is not requested and it remains red until you advance to the stop line.
If an emergency vehicle with blue light and emergency horn approaches that cannot be made room otherwise, the road user should, taking the necessary caution, drive just far beyond the stop line that the emergency vehicle can pass, and only if this is possible without a specific traffic hazard ( see right of way ).
If the traffic light shows yellow, you may continue to drive as an exception, but only if medium braking would no longer bring the vehicle to a stop in front of the stop line. If you brake hard in yellow, you are generally acting correctly. In these cases, a colliding vehicle is usually the main culprit behind the accident (due to insufficient safety distance ). This responsibility of the following is only excluded if the person braking consciously wanted to provoke a rear-end collision . However, without evidence ( witnesses ), such evidence will be difficult.
In the VwV-StVO (Germany), the duration of the yellow light phase is recommended as follows depending on the maximum permissible speed of the approach: 3 s for perm.v = 50 km / h, 4 s for perm.v = 60 km / h and 5 s for permissible v = 70 km / h (see § 37 point 17 IX. VwV on the StVO). The yellow light phase is called the emptying phase and clearing time, since during this time it should be possible to clear the following road section for traffic that will receive the green phase.
Green does not release you from the duty of care. Even if you think you neither have to slow down nor stop, there are special features. If the traffic light changes to green and there are still stragglers in the traffic light-regulated area (so-called protected area), they are generally given priority to clear the intersection.
At some intersections with high traffic density there is a separate circuit for turning in certain directions (green arrow), i. H. only this turning traffic is green and does not need to pay attention to oncoming traffic because it is stationary (so-called free traffic light).
However , traffic is usually only allowed to turn left if it does not hinder rail vehicles. That means, if you want to turn, you have to let oncoming vehicles pass through: Rail vehicles, bicycles with auxiliary engines and cyclists even if they are driving on or next to the road in the same direction. This also applies to regular buses and other vehicles that use marked special lanes. He has to show special consideration for pedestrians and if necessary he has to wait.
In order to save energy and costs, in the 1980s cities and municipalities switched to operating traffic lights only with flashing lights at times of low traffic ( night shutdown ). If a traffic light flashes yellow, the person entering the intersection is called upon to be more careful and may have to give others the right of way. The designated traffic signs apply. If there is a stop sign at a junction ( sign 206 ), you must stop at the stop line and, if necessary, again at the line of sight (Appendix 2, serial no. 67 to StVO). If, on the other hand, there is a sign 205 (give way!) At a junction, it is possible to turn into the street or cross the street without stopping beforehand. Before switching to yellow flashing , all traffic axes are often switched to red for a short time for safety reasons.
In Germany, deactivated traffic lights usually only flash in the secondary direction, in Poland, Italy, Austria and Switzerland the yellow flashing light is displayed for all directions.
In the USA and Canada, where there are usually no additional traffic signs for right-of-way control in the event of a traffic light failure, as in Europe, a red flashing light is displayed in the secondary direction, which has the meaning of a stop sign and obliges the vehicle driver to stop at the line of sight. Yellow flashing light ("Attention") is used in the main direction.
During the normal operation of traffic lights, yellow flashing light is also used as a Passive Permit Left Turn (PPLT) - the existing American technical term - to warn turners of oncoming traffic as well as pedestrians and cyclists. In rare cases a yellow flashing light is shown instead of green in an entire direction of travel (as in Augsburg at the station square). In France and Switzerland, traffic lights can be found at construction sites that have a yellow, flashing one instead of a green signal. Here the road user should be warned to be more careful. These yellow safety flashers are attached to the main signal in a separate housing and are provided with a directional arrow if the right of way for pedestrians only applies to the branching traffic and their pedestrian ford is also green parallel to the straight ahead direction.
When the pedestrian signal changes from green to red, all pedestrians who have already entered the lane should quickly cross the ford or continue to the next safe installation area.
The pedestrians' evacuation time begins with the start of red, which ensures that pedestrians can cross the entire secured area at a speed between 1.0 and 1.5 m / s (usually 1.2 m / s) to the next safe area . Only then will the traffic crossing the pedestrian ford be released. For drivers turning off, a pedestrian ford signaled in red does not mean that there are no pedestrians there.
If a common signal is used for pedestrians and cyclists, this results in unnecessarily long waiting times for cyclists, especially at large intersections, who could safely pass the intersection at the beginning of the red phase for pedestrians due to its higher speed. For this reason, an additional traffic light is often installed, which sometimes switches to red later. In the United States, cyclists can use the pedestrian signals that flash red just before they turn red and are often linked to a countdown that is counting down. If the pedestrian signal is already flashing, the cyclist knows that he has to accelerate in order not to have to wait. If the countdown has progressed to 2 (small intersection) or 5 (large intersection), the cyclist knows that there is no longer enough time to safely cross the intersection. The yellow signal for car traffic begins immediately with a steady red for pedestrians (immediately following "1" on countdown).
The signal color "yellow" is generally not used in Germany for pedestrian traffic lights. The exception to this is the city of Düsseldorf, where there are “red-yellow-green” signals for pedestrians. Some people are irritated by this yellow phase, which is why the city of Düsseldorf distributed an eight-page brochure. The topic was: “This is how you cross the street in Düsseldorf”.
Traffic light failure
If a traffic light fails, it is likely that it will no longer function properly in the entire intersection area. Built-in protective circuits therefore ensure that green is not displayed on two crossing lanes at the same time . In addition, it must be ensured that if the red light fails, a crossing lane is not displayed in green anyway. Usually a traffic light system either switches to flashing yellow or switches off completely. In order to regulate the flow of traffic anyway, traffic-regulating traffic signs are often attached next to the LSA. If police officers control traffic, their signs and instructions apply and take precedence over all other signals and traffic signs (even when traffic lights are working). However, the instructions in no way release road users from their own duty of care (in Germany, (2) StVO).
Legal meaning in Germany
In German traffic law, the general traffic rules apply initially, i. H. §§ 2 to 35 StVO . Traffic signs have priority over these according to StVO. The LSA, in turn, have priority over traffic signs according to (1) StVO. Signs and instructions from police officers are given priority to the traffic lights. The rules of conduct are laid down in StVO. Anyone who disregards the LSA acts in violation of the traffic regulations, (3) No. 2 StVO. If a driver crosses the stop line after the traffic light showed red for more than a second, there is a risk of at least a month's driving ban and a fine of at least 200 euros. For the monitoring of the red light of measures taken by the police and administrative authorities.
The road construction agency is responsible for setting up and maintaining the traffic light. The construction and operation of traffic light systems are described in the guidelines for traffic light systems (RiLSA) .
Suggestions for improvement
It is occasionally criticized that the crossing time of individual or numerous traffic lights is too short for pedestrians to safely reach the opposite sidewalk. This is particularly difficult for the elderly or sick, who can only walk slowly. From a legal point of view, the traffic light only has to be on "green" when entering the lane; if it then changes to "red" en route, the pedestrian can and should quickly complete his way to the other side, since the red phase of the crossing traffic flows is extended by a sufficiently long clearance time or at least it should be. The permissible and safe crossing time is accordingly longer than the green phase itself. Nonetheless, the entire crossing time including the buffer is sometimes perceived as too short, and it is also criticized that pedestrians cannot exactly know the end of it.
In the autumn of 2015, the city of Graz's road authority put the web-based traffic light assessment service “Traffic Check” into operation and received 800 responses with criticism and suggestions for improvement in the first week. Two thirds concerned motor vehicle traffic, one third pedestrian and bicycle traffic. Topics were "Green wave, waiting time for pedestrians and conflicts between bicycle and car traffic."
Special traffic lights
Heuer traffic light
The name Heuer-Ampel goes back to the inventor Josef Heuer and the company Heuer-Hammer , a processing plant in Iserlohn - Grüne . Heuer traffic lights are a special form of traffic light systems that were used from the 1930s to the 1960s in the Netherlands and Austria (Vienna), but also in Germany (e.g. Dresden, Albertplatz , from the 1930s). They are roughly cube-shaped structures that hung over an intersection with wire ropes . They were mainly suitable for simple conditions, for example when two streets crossed at right angles.
The internally illuminated traffic lights had a translucent disc for each direction of travel with opposite red and green circular segments. The traffic light phases were shown with a pointer driven by an electric motor that rotated slowly in a clockwise direction . The color to which the pointer pointed was valid. Since the pointers were linked on all sides (and thus had the same speed of rotation) it was almost impossible for signaling errors to occur. By manually interrupting the power supply, it was possible to stop the rotation during peak traffic times in order to achieve extended green phases for the main traffic direction.
There was no yellow intermediate phase. The pointer position showed how long the respective phase lasted. However, indirectly there was a yellow phase, as the red sections were larger than the green for safety reasons. This resulted in a brief overlap of the red phases.
The last Heuer traffic lights in Germany were up until 1972, after which the new traffic regulations no longer allowed traffic lights. The replica of a Heuer traffic light can be seen in Bochum at a historical location above the intersection of Bongardstrasse / Kortumstrasse. In Detmold, a device was restored that is now hanging on the entrance to the university there.
A very similar facility existed in Australia under the name Marshalite . This even had a yellow phase.
Dallas Phasing was a design of a five-field signal head for intersections with Passive Permit Left Turn (allows left turns, with oncoming traffic having priority) in Texas, which mirrored the green of oncoming traffic with a striped blackened green bezel. Dallas Phasing was introduced to prevent the "yellow trap" that occurred with signal heads on the opposite side of the intersection when the oncoming traffic was switched to different phases. In the 2009 Manual on Uniform Traffic Control Devices (MUTCD), Dallas Phasing was banned after 15 years and consistently replaced by the yellow flashing arrow.
The term “begging light” describes a phase-controlled traffic light with separate buttons for bicycle and pedestrian traffic. This is to be distinguished from a demand-driven traffic light. While the traffic on the lane has a green signal and can flow, there is a button with a separate signal for bicycle traffic on the adjacent area. Pressing the button causes the secondary area traffic light to receive a green signal together with the lane traffic light in the next phase. The buttons on the begging lights are sometimes viewed as unhygienic and can infect the pedestrians using them with infectious diseases such as the flu.
The police in Mumbai , India , have tested a traffic light system that is supposed to reduce the noise caused by honking road users. Decibel measuring devices were connected to the traffic light system . If they detect a reading of more than 85 decibels, the traffic lights stay red longer.
Red-yellow-yellow traffic light
In Göttingen-Weende there was a traffic light with two yellow signals. Instead of green, a permanent yellow signal was switched. This should enable learner drivers to leave a parking lot safely, but this signaling was not compliant with the current German road traffic regulations. For this, the yellow light should have flashed, which was not the case with this traffic light.
Permanently red traffic lights
From 1987 to 2016 there was at least one traffic light in Dresden in connection with a green arrow, which showed permanently red. It should prevent prohibited left turns at this point. A simpler solution - for example a stop sign and the 209 sign - was not possible because there must be a traffic light system at every entrance to a traffic light controlled intersection.
Traffic lights in art
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- Traffic Light Tree by Pierre Vivant in London.
- LISA + (software for traffic control)
- VS-PLUS (model-based control method)
- Formula 1 starting lights
- Bompel (floor traffic light)
- Bike flash
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