At a time when cities across the world seek ways to reduce traffic, the mayor of Romania's capital Bucharest has launched an ambitious project to build a new motorway in the city, despite widespread protests.

At a cost of 1.5 billion euros ($1.9 billion), the six-lane freeway will be 13 kilometres (eight miles) long and cut through several residential districts.

Notably jacking up the cost is a plan to have it cross under one of Bucharest's largest parks, Herastrau.

"This means one kilometre will cost more than 100 million euros, whereas the European average is around five million," said Nicusor Dan, president of the Save Bucharest association.

Mayor Sorin Oprescu has made the project the top priority of his second four-year term which ends in 2016.

"The funds will not come from our budget," he pledged after the city council approved the draft plans. "The motorway will be built under a public-private partnership."

Chinese, US, Russian and South Korean investors were interested in the deal, Oprescu said.

Last year the mayor even signed a memorandum to this effect with the Shanghai Construction Group.

If urban motorways remain popular in Asia's big cities, in western Europe the priority is increasingly to curb traffic.

"In the short run, a new motorway does tend to relieve traffic congestion, but after a while it only attracts more cars," Gruia Badescu, a town planning expert and doctoral student at Cambridge, told AFP.

After experiencing similar problems, several French cities such as Marseille and Grenoble decided to bulldoze bridges crossing built-up areas.

Back in the 1960s, municipal authorities in Paris planned to build a network of urban motorways but gave up the idea before any harm was done to the City of Lights.

Now, the coalition of French Socialists and Greens which has the majority in the city council promises to turn a road running along the Seine through the heart of Paris into a riverside promenade in 2013.

"Western Europe is increasingly calling into question not only the omnipresence of cars but also the extensive development of cities," Jean Laterrasse, head of the city transport lab of Paris Est university, told AFP.

Instead, "Bucharest is facing two major problems -- on the one hand the lack of town planning administrative culture and on the other the absence of dialogue between authorities and the community," said Gabriel Pascariu, a professor at Bucharest's Ion Mincu architecture university.

"Recent studies have shown that traffic is not the topmost problem to Bucharesters," he added.

A Balkan town that turned into a metropolis under the communist regime has some two million inhabitants and is an economic hub of southeastern Europe.

-- '1970s solutions can't solve trffic jams today' --

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Bucharest, disfigured when the late communist dictator Nicolae Ceausescu razed three-quarters of its historical centre to build a gigantic palace, has in recent years fallen prey to real estate predators and is suffocated by traffic.

In the middle of the last decade, when Romania was enjoying an unprecedented economic boom, more than 1,000 vehicles were registered daily in Bucharest.

The number of cars has doubled in the past 10 years and now tops one million.

"It's obvious that solutions that worked in the 1970s cannot solve traffic jams today," said Alain Bourdin, a town planning professor at Paris Est university.

"But we have to be realistic: authorities cannot limit traffic unless they provide a very dense public transportation network," he added.

In Bucharest, while the mayor has decided to make life easier for drivers, associations fighting to preserve the city's architectural heritage are siding with pedestrians and bicyclists.