* Brussels named developed world's most congested city by INRIX
* EU traffic congestion costs estimated at 100 billion euros
* One solution would charge drivers by distance travelled
* Trials under way
By Philip Blenkinsop
BRUSSELS, April 27 (Reuters) - For two years running, Brussels has been named the most congested city in North America and western Europe, a mark of shame for the capital that guides Europe's environment and transport policies.
The disgrace has, however, had the effect of uniting Belgium's environmentalist Green Party, centre-right rivals N-VA and business and motoring groups in a call for a solution whose time may finally have come - charging drivers for distance travelled. Tests have already begun.
Others are watching keenly to see what will work in a city the size of Brussels, whose issues are different from sprawling megacities like Bangkok or Beijing, or London, with its central congestion charge.
"Since London brought in their congestion scheme, technology has come a long way," said Nina Renshaw, deputy director of sustainable transport campaign group Transport & Environment.
"Today it's possible using GPS (global positioning systems) to have precise billing per kilometre which wasn't possible even 10 years ago," she said. "That makes it much more attractive for cities to consider it."
Cities in the Netherlands and Sweden are among those who want to reduce congestion but also cut carbon emissions, an effort in which Europe sees itself as setting an example.
The European Commission estimates traffic congestion costs at nearly 100 billion euros per year, or 1 percent of the European Union's gross domestic product, not including the health costs of pollution.
The latter has led to the rise of low emission zones in cities from Umea in northern Sweden to Naples in southern Italy. Air pollution from traffic prompted Paris to ban cars with even number plates from entering the city for a day in March.
Bruno De Lille, Green Party member and mobility secretary for the Brussels region, is sceptical his city really is the developed world's capital of congestion, as traffic services provider INRIX says, but acknowledges his city has some unique problems.
One is Belgium's high population density, ranked 10th in the world, excluding small island or city states such as Malta or Singapore.
It also has a tax system that encourages company cars and compensates the cost of driving to work, with the former taxed at a lower rate than salaries and the latter able partially to be offset against tax.
Moreover, more than half of the 650,000 people employed in Brussels live outside city limits.
Around half of those commute into the city by car, a higher proportion than in most European cities. Eurostat data shows the same figure in Amsterdam is 40 percent, for example. In Washington DC, the percentage is also around 40 percent, and for Chicago, it is 50 percent, according to the U.S. Census Bureau.
So far Brussels has tried to fight traffic creep by making public transport more attractive with special bus or tram lanes. That has worked by convincing many commuters to switch to public transport or bicycles, but has also created its own problems.
"What we've seen in the last 10 years is that we've got 7 percent fewer cars on the roads, but the jams have got longer. That's because there's less room for cars," De Lille said.
On weekday mornings, there are a combined 150-200 km (93-124 miles) of jams on 7,000 km of Belgian highways on average, according to motorist association Touring. The record, set on one day in March last year, was 1,400 km of jams.
The most common way of tackling traffic congestion, and the pollution it causes, has been a congestion zone, such as those in place in London, Stockholm and Milan.
London's 10-pound charge has reduced car traffic by 27 percent since its introduction in 2003. Milan dropped off the top of the INRIX congestion standings after it introduced a charge in 2012.
Brussels is considering a combination of steps, including a rapid regional rail system along the lines of Paris's RER.
"But if we want the cars to move more freely then we have to take another step," De Lille said.
The proposal to charge drivers per kilometre travelled is already on trial with around 1,000 volunteers in the city and neighbouring regions of Flanders and Wallonia.
In the trial, the volunteers' driving patterns and distances are measured. If they subsequently drive less they are rewarded with cash, while activity over the norm is noted. In real life, people would be charged electronically or via ticketing for driving during peak hours.
The idea is backed by the Flemish separatist party N-VA, currently the largest party in parliament, albeit balanced against reductions of annual road tax, as well as business bodies, the Belgian auto federation Febiac and Touring.
First public responses have been negative: an online petition opposing the scheme quickly gained over 170,000 signatories.
In the past decade, plans for congestion charges in Manchester and Edinburgh were rejected in referendums.
But Transport & Environment says public opinion can shift sharply once road pricing is set up. In Stockholm, for example, a poll showed very strong support for its congestion charge a year after its launch.
Transport & Environment also says that a kilometre charge is a more effective way to cut congestion and emissions than a congestion charge which some users simply get used to.
"We prefer the kilometre charges because if you pay a one-off fee you're incentivised to maximise your driving within that period," said Transport & Environment's Renshaw.
Jeroen Verhoeven of Bral, a group seeking to make Brussels more liveable, believes a combination of congestion zone and distance charge would be best.
With just the former, there is no discouragement to drive after taking the one-off hit. With just the latter, drivers may still be inclined to make short trips in the city.
Joost Kaesemans of Febiac, who says he regularly cycles to work, says the time lost to traffic jams has doubled in Belgium since 2007.
In a report with PwC last year, Febiac said cutting traffic by just 5-10 percent could reduce congestion by 40 percent.
"Road pricing is a system you can influence yourself. We estimate that 20 percent of the peak-time traffic doesn't have to be there at that time," he said.
"Is it for tomorrow? It could take until after 2020 ... but doing nothing is not an option." (Editing by Sonya Hepinstall)