Warning sign

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Some of the first roadside signs—ancient milestones—merely gave distance measures. Hazard warnings were rare though occasional specimens appeared, such as the specific warning about horse-drawn vehicles backing up which was carved in stone in Lisbon's Alfama neighborhood in 1686. The early signs did not have high-contrast lettering and their messages might have been easily overlooked. Signs were written in the local language (example); symbolic signs, though long used on certain tradesmen's signs (like the pawnbrokers' tri-ball symbol) were to be used for traffic only much later in history.

Complex signage systems emerged with the appearance of motorcars. In 1908 the automobile association in West London erected some warning signs. In 1909, nine European governments agreed on the use of four pictorial symbols, indicating bump, curve, intersection, and railroad crossing. The intensive work on international road signs that took place between 1926 and 1949 eventually led to the development of the European road sign system.

As the 20th century progressed, and traffic volume and vehicle speeds increased, so did the importance of road sign visibility. Earlier flat-painted signs gave way to

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In Europe, 1968

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In modern regulations, U.S. warning signs are classified as Series W signs, such as W1 Series (curves and turns), W10 Series (railroads), et cetera, ending with the W25 Series (concerning extended green traffic lights). Some U.S. warning signs are without category while others like the warning stripes at tunnel portals or plain red End of Roadway signs are classified as Object Markers (OM Series). In the U.S., Stop and speed limit signs fall under the R Series (Regulatory). Modern U.S. signs are widely standardized; unless they are antique holdovers from an earlier era, oddities like a yellow Stop sign or a red Slippery When Wet sign would typically appear only on private property—perhaps at a hospital campus or in a shopping mall parking lot.

added to the outstretched hand of the Pedestrian Crossing person, for example.

Modern traffic warning sign shapes and colors

Warning signs can indicate any potential hazard, obstacle or condition requiring special attention. Some of the most common warning signs are the following.

General caution

General warning signs are used in instances in which the particular hazard, obstacle or condition is not covered by a standard sign. In Europe, they usually comprise an exclamation mark on the standard triangular sign (Unicode U+26A0 ⚠ WARNING SIGN) with an auxiliary sign below in the local language identifying the hazard, obstacle or condition. In Sweden, the general warning sign has only a vertical line instead of exclamation mark; this model was used also in many other European countries until the 1990s. In the United States and other countries using diamond-shaped signs, the explanatory language is often written directly on the diamond-shaped sign, although it may contain only a general warning such as "Caution", and pictograms may also be used.

Obstacles

Warning signs can be placed in advance of, next to or on a specific obstacle. Obstacles such as railway level crossings may have several warning signs beforehand, while bridge ramparts typically have reflective signs placed directly on them on either side. These signs can be specific to the shape requirements of the obstacle, for example, bridge rampart signs are often tall and skinny so as not to intrude into the lane.

Curves and corners

These signs indicate that dangerous or unexpected bends in the road are ahead. Signs typically indicate whether the curves are to the right or to the left, the angle of the curve and whether it is one curve or a series of curves.

Chevrons and arrows

Chevron-shaped symbols or arrows on rectangular signs may be placed at the actual location of the bend or curve to further mark the location of the curve and to assist in the negotiation of the curve. They may also be used to indicate "merge" with other traffic, as for an on-ramp of a limited-access highway.
An unusual occurrence of the rectangular arrow sign appears on the eastbound approach to

, US, a curve so sharp that in places an arrow's stem is printed on one sign and the arrow's point is printed on another larger sign further down the road; from the driver's perspective at a distance, the two signs visually blend together to form one large arrow image.

Steep hills

Truck drivers will need to pay attention to "Steep grade" warnings (or "Down grade, use lower gear"), sometimes posted with the percent grade (e.g., 5%). Steep hills may also feature "Runaway truck escape" or "Emergency stop" areas with corresponding signs. The

" on a curve.

Lane starts and ends

These signs indicate when a multilane highway is being narrowed, when a passing lane is ending, or where the road is widening or a passing lane starting. Another type of sign is used to indicate central "two-way" left turning lane in center of roadway. Warning signs may also warn of "Highway ends", where the road changes class or type.

Merge to stay with through traffic

In the United States and Canada, there is special signage for lanes that are about to exit, so that drivers who wish to remain on the main road have adequate time to merge. Such lanes are sometimes indicated by special striping ("alligator stripes") and the sign, "Through Traffic Merge Left" (or right). On freeways, the green directions sign for the exit ramp may have the additional notation, "Exit Only", and should have black letters on a yellow background for emphasis.

Bridges

These signs are used where traffic may be constricted to a narrow bridge, or where the bridge may have a movable span closed to vehicles while boats pass (e.g., drawbridge). They may also be used for underpass to indicate low overhead clearance.

Tunnels

These signs are used to indicate tunnels, where lights are usually required, and a general change in the light level. May also indicate low ceiling clearance. Truck drivers should also watch for prohibited cargo signs (e.g., propane) upon approach to tunnels.

Road conditions

Warns road users of severe road conditions ("Icy road", "Bump", etc). Also "Loose gravel", "Soft shoulder", "

", and "Watch for ice".

Falling rocks

These signs may be used to indicate the hazards of fallen or falling rocks on the road ahead. They are usually pictographs, but may also include wording, such as "falling rocks". In Italy the words may be "caduta sassi" or "caduta massi"; in France "chute de pierres"; in Mexico "derrumbes".

Pedestrian crossings

These signs are used to warn drivers of people walking in the street. They may also be used to warn of children playing, playgrounds, bicycle area, deaf child, blind pedestrians, and thickly settled zones where pedestrians may enter the road.

In

Schools

These signs mark school zones (in which lower speed limits may be in place), student crossings, crossing guards or signals ahead. In the U.S. and Canada, pentagon-shaped signs are used in place of the usual diamond-shaped signs. The shape of the U.S. school zone resembles a

and is the only U.S. sign shaped this way. Some Canadian provinces use an identical sign.

Bicycles

Bicycle crossing signs warn that bicycles will cross at their location.

Animals crossing the roadway

These signs warn of wild animals (deer, etc.) or farm animals (cows, horses, ducks, sheep) that may stray onto the road. In the United States, a "share the road" plaque is sometimes placed below these warning signs when used in this manner.

Unusual vehicles in roadway

These signs are found where road users could encounter slow, large or non-typical vehicles such as forklifts, handcarts and military vehicles. They are more common around quarries, airports, industrial zones, military installations and rural areas.

Road work or construction

These signs are often temporary in nature and used to indicate road work (construction), poor roads, or temporary conditions ahead on the road including flagmen, uneven pavement, etc. (Note that some "high water" signs are posted to alert drivers of a flood-prone area and do not actually mean that there is a flooded section of road ahead.) In France, Italy, Spain, Norway etc., warning (and speed limit) signs connected with road work have a yellow background in place of the usual white background on signs. In North America and Ireland, signs connected with road work have an orange background.

Traffic signals

These warning signs indicate that

, fire stations, and airfields.

Intersections

These signs warn of road crossings at crossroads, T-intersections, roundabouts, or Y-intersections. They may also indicate "hidden driveway" intersecting the road ahead. (Compare with bridges, overpasses, viaducts).

Warning signs for regulatory signs

Like for traffic signals, some "stop" or "yield" signs may require additional warning or reminder, especially in dense areas or where the sign has been added recently.

Oncoming traffic

These signs may be used to warn people of oncoming traffic; shown when a

or median.

Level crossing (railway crossing)

These signs are used to warn of level crossings ahead. In most countries, a red triangle warning sign is used, with various pictograms for unguarded crossings, crossings with manual gates, and automatic level crossings. In most of Europe, an old-style gate is used for a crossing with gates, and a steam locomotive for a crossing without gates. Germany uses an electric train. Similar pictograms are also used in Ireland, albeit on an amber diamond sign. In the United States the warning of all types of railway crossings is made using a circular yellow sign. The actual crossing is also marked with crossed "railroad crossing" crossbuck signs (stop, look, listen) and possibly lights, bells, and barriers.

Low flying aircraft

A warning sign with the image of an aircraft in the middle of it indicates an airport or airfield, where drivers should be prepared for low-flying aircraft.

Crosswinds or side winds

Flying socks, as indicated in Poland by a windsock on red triangle or yellow diamond signs, indicate locations where a strong side wind may cause the trajectory of the moving vehicle to change drastically, perhaps even "flying" across lanes, causing an accident.

Roads with one entry point

Roadways that only have one entry/exit point - "

", "not a through street" or "no outlet".

End of roadway

Signs indicating the end point of a

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Fire stations

These signs warn of approach to where

or other emergency apparatus, where other drivers will have to stop and wait until they pass.

Traffic warning signs with lights

Some warning signs have flashing lights to alert drivers of conditions ahead or remind drivers to slow down. In

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• Attached lights
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  School zone traffic warning sign in Denmark.
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  A traffic signal ahead sign in France. (the light flashes to indicate a red light ahead)
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  A pedestrian crossing sign in the United States with solar-powered lit outline.
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  A portable multipurpose traffic warning array in Denmark, displaying Ulykke ("accident") and "keep right".
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  A school zone sign in the United States. When the light flashes, the set speed limit (in this case, 25 mph (40 km/h)) is active.
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  A "Watch for Water on Road" sign in the United States.

See also

References

External links

• Media related to Warning signs at Wikimedia Commons