Motorists in five European nations will be offered live warnings about snarled roads starting this autumn as car navigation gets smarter, Dutch manufacturer Tomtom said at the IFA trade show in Berlin on Thursday.

The maker of satellite-navigation devices is to use data gathered from cellular phones by the mobile company Vodafone.

Cellulars constantly report their positions to a phone company's transmitting towers. A large number of phones stationary on a busy highway is assumed to mean that many motorists are stuck there in a traffic jam.

Vodafone's HD Traffic project to sift the signals for traffic data has already begun in the Netherlands.

Tomtom said its new Go x40 Live series of devices would also contain telephone SIM cards reporting back global positioning (GPS) information and giving a true indication of how fast traffic is moving at any hour of the day.

The Dutch company expects to obtain vast amounts of data. Corinne Vigreux, managing director, said Tomtom had already obtained 200 billion road speed measurements from its customers.

For a monthly fee of 10 euros (15 dollars) Tomtom is to use that data to predict congestion and guide motorists around it.

While Tomtom made no claims about an industry first, specialist journalists at the IFA trade show said it was the first major manufacturer to offer a truly live GPS device. Existing products rely on police logs which describe main highway congestion only.

Tomtom said the product would launch in Germany, Britain, France, Switzerland and the Netherlands.

Motorists would also be able to punch in warnings about police radar surveillance and send this automatically to Tomtom computers, so that other Tomtom users could slow down before they come in range of the speed cameras.

However this service would not be offered in Switzerland, where it is illegal to communicate warnings about speed traps.

The 349-euro (517-dollar) device was introduced at IFA, one of the world's main annual shows of consumer electrical products. IFA opens Friday and will run until Wednesday next week.