A new service that combines sat nav and mobile phone technology is set to become the most potent jam-buster on the road.

It will allow drivers to view real-time images of traffic hotspots and will direct them towards alternative routes. The maker claims it will also signal the end of phantom jams caused by out-of-date traffic information being sent to conventional sat nav units, directing drivers away from congestion long since cleared.

The new device was previewed last week by the Dutch maker TomTom, and will be available in Britain early next year. Like all clever ideas it’s actually very simple, relying on the fact that millions of drivers carry mobile phones that broadcast signals, showing not only where they are, but also how fast they are moving. By crunching this data, TomTom and its partner Vodafone hope to provide the most accurate picture yet of what’s happening on the roads, and warn drivers if they’re about to face slow-moving or static traffic.

The system picks up mobile signals in the vicinity of, say, the M1. It filters out signals from pedestrians or cyclists by using software that recognises movement patterns, leaving only signals from drivers. By analysing the changing position of each signal, the technology then determines whether or not cars are moving freely.

This information is then relayed over the mobile phone network to in-car sat navs so that drivers can see on a real-time map exactly where the trouble spots are and how fast vehicles are moving across the road network.

Many existing sat nav systems claim to be able to warn drivers of congestion ahead, but few work well because they rely on unreliable or out-of-date information.

In Britain there are currently two main sources of such information. Trafficmaster relies on data from some 7,500 roadside cameras and sensors fixed to bridges, which monitor traffic speed then send out alerts whenever it drops below 30mph. The second company, Itis, relies on “floating vehicle data”, where GPS tracking is fitted to vehicle fleets such as National Express coaches and AA vans. In both cases, once information has been collated, it is broadcast by radio to the sat nav in the car.

The problem is that the camera network is patchy, particularly on minor roads, while the floating traffic data can only give a partial snapshot of the true situation. In addition, the radio frequencies used limit the amount of information that can be sent.

Drivers are aware of the drawbacks and these days there’s a familiar debate about whether you should obey the traffic warning system and take an alternative route, or simply ignore it on the basis that it is probably wrong.

TomTom says its service, known as High Definition (HD) Traffic, gets around these obstacles because anyone with a Vodafone mobile phone (that is switched on) becomes an information provider. And because traffic information is relayed over the phone network, which can send almost unlimited amounts of data, the sat nav can be updated far more regularly. The company says this means five times more traffic updates than previously available, and a tenfold increase in the number of roads covered.

Last week I visited the company’s headquarters in Amsterdam for an exclusive road test of the technology. To see how it handled rush-hour traffic, we drove to a ring road around the city. Before me the unit displayed the distance to a traffic jam, the time it would take to reach it, and how long the delay would last. We were told it would be two minutes to reach the jam, and that we would be delayed by four minutes; it was right about both.

“We’re not saying you’ll always get to work faster, as sometimes avoiding congestion is impossible,” said Luciën Groenhuijzen, the TomTom executive in charge of the project. “But a couple of times a week, when there is a serious jam, you may gain 20 minutes through our device finding a faster route.” The first gadget to use the system, the TomTom One XL HD Traffic, will go on sale in Holland at the end of this month and cost €399 (£285), and is expected to be similarly priced when it is launched in Britain in the new year. TomTom is also working on a hardware add-on that features a Sim card (needed to connect the sat nav to the mobile phone network) enabling people to keep their existing sat nav while still benefiting from the HD service.

Whether Vodafone’s 16m UK customers want to be tracked is another matter. Under the terms of the deal between the two companies, phone users will have no choice but to make their location available, prompting questions about individual privacy.

It’s already been established that the police can use mobile phone data to track people’s locations and movements, so putting this information in the hands of a private company is likely to raise concerns, although Groenhuijzen says he can’t track people with it, as the information is anonymous and can’t be linked to individual identities.

“We have already been inundated with queries from people asking if we can track them, but we can’t,” he says.