The former Transport Minister and London mayoral candidate Steven Norris says the case for replacing our current simple system of fuel tax with something more advanced has never been stronger and there is good reason to think that its time might finally be coming.Writing on the "London Essays" website, the ITS (UK) President argues that road-user charging can achieve what fuel duty cannot: it can impose higher costs on journeys that have the greatest negative impacts ' journeys on already busy roads, or journeys through highly built-up areas.  He adds that varying charge rates can be deployed to spread flows more evenly throughout the day or to encourage motorists to use more suitable routes."It is doubtful whether Londoners, in particular, would have approved of the Congestion Zone had Mayor Livingstone ever made the mistake of asking them before he introduced it in 2003," he writes.  "When similar schemes were put before voters in Edinburgh in 2005 and Manchester in 2008, the vast majority voted against them. It is not surprising, then, that it is hard to find many politicians ready to argue for road-user charging."Mr Norris adds that, while road-user charging would be helpful to transport authorities everywhere, it could prove particularly helpful to London.  He explains that road space is in especially short supply in the capital and, with its population growing faster than at any time in its history, the pressures on road space are only going to intensify.After writing about his views on the current Congestion Charge in London, Mr Norris finishes with these words: "Road-user charging will happen if not in this Parliament or the next, then at the point where a future Chancellor faces the precipice of lost receipts and concludes that there is, in Margaret Thatcher's immortal words, no alternative."You can read the entire essay here.