Transport experts who gathered at the city's university were told the continuing development of in-car technology meant that levying motorists for the number of miles they drive could become a reality by 2020.
Frederic Bruneteau, one of the speakers at the Intelligent Transport Systems conference, said that increasingly over the past 18 months motorists have been buying sat navs or smart phones with a two-way connection.
He said the devices, which allow drivers to receive and send information about traffic and weather, were still relatively expensive today.
But, he said, by 2020 it is predicted they will be the norm, which could allow governments to charge motorists variable road tax depending on how far they drive.
Mr Bruneteau, who is managing director of Brussels-based navigation consultancy Ptolemus and who formerly worked for Vodafone and sat nav firm TomTom, said the 'e-tolling' technique was already being used in long- haulage trucks in Europe.
He told the conference that the same could apply to private cars if governments were serious about cutting down road journeys and slowing climate change.
Mr Bruneteau said: 'Instead of everyone paying the same road tax, drivers will pay depending on how far they drive. So if you drive less, your road tax will be lower. People can then see a real financial gain which should encourage people to drive less, which is better for the environment.
'Road haulage trucks in Europe already do this. There are projects looking at it for cars in Sweden and France. In the Netherlands there are 200 people in the government working on it.'
But while the technology will be widespread by 2020, and European nations are exploring its uses in the run- up to the United Nations climate change conference in Copenhagen next month, Mr Bruneteau said moves towards e-tolling in the UK were slow. He said: 'There's no certainty it will happen. Such a system would need to be robust if it's to be done on a wide scale.
'But the technology is there.
'It's whether there will be the political will to do so. Britain is lagging behind many European countries for the moment.'
HI-TECHHi-tech CCTV that is being used to spot criminals before they strike could be used to ease motorway traffic jams before they become a problem.
The technology is being used in Portsmouth's CCTV control room and is programmed to watch out for certain suspicious behaviour or incidents.
This could include a car being driven at excess speed, someone loitering for longer than normal in a car park, or people coming together in known drug-dealing areas.
The Perceptrak system, produced by Smart CCTV Ltd of Havant, then sends out an alert if it records something suspicious.
Speaking at the Intelligent Transport Systems conference at the University of Portsmouth, the firm's managing director, Nick Hewitson, said such technology could be used to ease congestion on motorways, including the M27.
Mr Hewitson said: 'If the system sees a car break down on the hard shoulder then a call can be sent to the AA for a recovery vehicle to remove it before it slows down too much traffic.
'It's done automatically, rather than depending on human observers who get bored watching hours and hours of CCTV. The technology won't stop congestion but it will reduce the length of time people are stuck in jams.'
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