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BRUSSELS (AP) — How do you unify a half-billion people from the Azores to the Arctic? Europeans balked at a continent-wide constitution. EU officials hope license plates might help do the job.

This summer, Europe's vacationers are hitting the highways with more or less uniform plates, after 12 years of slow-as-syrup and at times impassioned debate over color schemes and the EU's role in everyday life. Belgium finally settled a political argument over the tags in June, clearing the last major hurdle to introducing the new plates in all 27 EU nations.

However, "uniform" is a relative term in a union with dozens of official languages and dozens of ways to say "license plate," and there are already exceptions to the suggested EU standard of black-lettering-on-white-background and a European flag on the left. Britain, as usual, is among the outsiders — drivers there get to opt out altogether.

Such handwringing over something as seemingly basic as license plates illustrates why Europe's national governments have such a hard time agreeing on weightier matters like farm subsidies and immigration.

But EU bureaucrats say plates are serious business.

"People can get really emotional about (license plates)," says Belgian Transport Ministry spokesman Jan Pauwels.

Drivers still show their nationalities on the EU plates, in the form of a country code tucked inside the ring of gold stars on the EU flag, or just below it: D for Deutschland (Germany), NL for Nederland (the Netherlands), S for Sverige (Sweden), E for Espana (Spain) and so on.

Issuing nations may also allow local or regional heraldic symbols. For motorcycles, there is a square EU-style tag.

Don't look for catchy US-style slogans.

"Live Free or Die" (New Hampshire), "World Famous Potatoes" (Idaho) or "Discover the Spirit" (North Dakota) would probably go against European sensibilities.

One option might have been "In Varietate Concordia" ("United in Diversity"), the EU motto that is available in Latin and the union's 23 languages, but no one chose to go there.

In 1998, EU officials "recommended" uniform black-on-white tags that would be more readable and embody the union's single market. The EU plates help cameras spot speeders, tax dodgers and cars zipping through electronic toll booths in a continent with largely open borders.

Most EU states, and even neighboring non-member Norway, now make EU license plates mandatory.

But there's lots of wiggle room.

In Finland, Sweden, Cyprus, Denmark and Britain the plates are available but optional. British drivers are entitled to show their aloofness from Europe by replacing the EU flag with those of either England, Scotland or Wales.

Paul Watters, head of public policy at Britain's Automobile Association, said few UK motorists choose the EU flag.

"The government has allowed us to have the freedom to choose to display national flags," he said. "We wouldn't want to see the EU flag become compulsory in the U.K."

France began issuing the EU tag in 2009 and also tried to drop traditional regional indicators, to avoid stigmatizing drivers from less fashionable areas.

Parisian cars carried the number 75, while 93 meant nearby Seine-Saint-Denis, part of Paris' restive suburbs with their large immigrant population.

Richard Mallie from the French "departement" of Bouches-du-Rhone (Number 13) and 230 other French lawmakers rebelled, insisting the departement number was "a matter of roots, of attachment to an area."

They won. Curiously, French drivers can now pick any department number they like. Mallie says 75 percent still opt for their departement of residence.

In Belgium, the most ardent proponent of European unification and home to the EU headquarters in Brussels, the EU tag sparked a two-year spat between Dutch and French-speaking politicians, reflecting the country's broader bi-cultural rift. The French speakers rejected black-on-yellow tags as they are the colors of Belgium's Dutch-speaking north. Both sides nixed black-on-white.

In June, Belgium decided its trucks would adopt the EU plates, but passenger cars could have dark red letters instead of black.

Denmark opted for a black-on-white EU plate but proudly put a red rim around it, hinting at its red-and-white flag.

Europe's shift to standard license plates my sound innocent — and reactions overly excited — but the shift is akin to the U.S. federal government ordering coast-to-coast standardized license plates in lieu of state-specific tags.

EU spokesman Dale Kidd said there is no attempt to create "a single EU registration system (by) abolishing national license plates" as governments continue to decide on the number-and-letter combinations.

In the 1990s, EU officials sensed a backlash to what former British Foreign Secretary Douglas Hurd called a "European superstate inveigling its way into every nook and cranny of Europeans' lives." That backlash would be blamed in 2005 for the death of the EU constitution.

In the 1980s, EU governments engaged in a five-year debate over the EU passport before settling on gold lettering on a "Bishop Red" cover.

Choosing the design of the EU flag — 12 gold stars in a circle on a blue field — was a seven-year saga in the 1950s.

In 1993, "Ode to Joy," the 4th movement of Ludwig van Beethoven's 9th symphony, became the EU anthem, more than two decades after the idea was mentioned.

Neither the flag nor the anthem made it into the proposed EU constitution, which was rejected in 2005. Nor were they — much less the license plate standards — included in a watered-down successor treaty that took effect this year.