Trade restriction
A trade restriction is an artificial restriction on the trade of goods between two countries. It is the result of protectionism
Protectionism is the economic policy of restraining trade between states through methods such as tariffs on imported goods, restrictive quotas, and a variety of other government regulations designed to allow "fair competition" between imports and goods and services produced domestically.This...

. However, the term is not uncontroversial since what one part may see as a trade restriction another may see as a way to protect consumers from inferior, harmful or dangerous products. For instance Germany required the production of beer to adhere to its purity law
The Reinheitsgebot , sometimes called the "German Beer Purity Law" or the "Bavarian Purity Law" in English, was a regulation concerning the production of beer in Germany. In the original text, the only ingredients that could be used in the production of beer were water, barley and hops...

. The law, originally implemented in Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

 in 1516 and eventually becoming law for newly unified Germany
Unification of Germany
The formal unification of Germany into a politically and administratively integrated nation state officially occurred on 18 January 1871 at the Versailles Palace's Hall of Mirrors in France. Princes of the German states gathered there to proclaim Wilhelm of Prussia as Emperor Wilhelm of the German...

 in 1871, made many foreign beers unable to be sold in Germany as "beer". This law was struck down in 1987 by the European Court of Justice
European Court of Justice
The Court can sit in plenary session, as a Grand Chamber of 13 judges, or in chambers of three or five judges. Plenary sitting are now very rare, and the court mostly sits in chambers of three or five judges...

, but is still voluntarily followed by many German breweries.

Rectangular headlamp
A headlamp is a lamp, usually attached to the front of a vehicle such as a car or a motorcycle, with the purpose of illuminating the road ahead during periods of low visibility, such as darkness or precipitation. Headlamp performance has steadily improved throughout the automobile age, spurred by...

s were promoted in the United States where round lamps were required until 1975. By 1979, the majority of new cars now had the rectangular
In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...

 headlamps. Again, the U.S. permitted only two standardized sizes of rectangular
In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...

 sealed-beam lamp: A system of two 200 mm x 142 mm high/low beam units corresponding to the existing 7" round format, or a system of four 165 mm x 100 mm units (two high/low and two high-beam) corresponding to the existing 5¾ inch (146 mm) round format.

In 1968 the U.S. DOT
United States Department of Transportation
The United States Department of Transportation is a federal Cabinet department of the United States government concerned with transportation. It was established by an act of Congress on October 15, 1966, and began operation on April 1, 1967...

 outlawed any decorative or protective element in front of the headlamps whenever the headlamps are switched on. Glass-covered headlamps, used on e.g. the Jaguar E-Type
Jaguar E-type
The Jaguar E-Type or XK-E is a British automobile, manufactured by Jaguar between 1961 and 1975. Its combination of good looks, high performance, and competitive pricing established the marque as an icon of 1960s motoring...

, the pre-1968 VW Beetle, the Porsche 356
Porsche 356
The Porsche 356 was the company's first production automobile. It was a lightweight and nimble handling rear-engine rear-wheel-drive 2 door sports car available in hardtop coupe and open configurations. Design innovations continued during the years of manufacture, contributing to its motorsports...

, the Citroën DS
Citroën DS
The Citroën DS is an executive car produced by the French manufacturer Citroën between 1955 and 1975. Styled by Italian sculptor and industrial designer Flaminio Bertoni and the French aeronautical engineer André Lefèbvre, the DS was known for its aerodynamic futuristic body design and innovative...

 and Ferrari Daytona
Ferrari Daytona
The Ferrari 365 GTB/4, better known by the unofficial name Ferrari Daytona, is a Gran Turismo automobile produced from 1968 to 1973. It was first introduced to the public at the Paris Auto Salon in 1968 and replaced the 275 GTB/4...

. therefore had to be equipped with uncovered headlamps for the US market, further altering the look of European models sold in the United States. This change meant that vehicles designed for solid aerodynamic performance could not achieve it for the US market. In 1984, the DOT changed this rule, allowing replaceable-bulb headlamps of nonstandard shapes. However, this change did not mean that an automaker could equip a vehicle with the same type of headlamps in the US as in the rest of the world. United States headlamp standards are governed by Federal Motor Vehicle Safety Standard 108
Federal Motor Vehicle Safety Standard 108
Federal Motor Vehicle Safety Standard 108 regulates all automotive lighting, signalling and reflective devices in the United States. Like all other Federal Motor Vehicle Safety Standards, FMVSS 108 is administered by the United States Department of Transportation's National Highway Traffic Safety...

, which is incompatible with the UNECE standards
World Forum for Harmonization of Vehicle Regulations
The World Forum for Harmonization of Vehicle Regulations is a working party of the United Nations Economic Commission for Europe...

 used in most of the rest of the world. Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

has its own headlamp standards similar to the US standard, but allows UNECE-compliant headlamps. Also Headlamps were not only used in cars but also used for traffic violation stops.
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