This system is fairly poor in the UK. It has an ostensibly useful feature whereby local radio stations transmit a flag to say they're currently broadcasting traffic information. This then instructs car radios to interrupt what the listener can currently hear (eg. a CD, a national broadcast) and play the traffic bulletin from the local station. Sounds useful.

In practice, FM radio signals travel so haphazardly that in most areas, you're likely to be interrupted several times an hour with travel news for towns and cities 40, 50, 60 miles away. I regularly get the bulletins for places as far afield as Shropshire, Humberside, Merseyside and Lincolnshire. If, while driving, the signal becomes too weak for the 'traffic off' flag to be received, the radio will simply stay tuned to the FM frequency until the listener manually cancels it.

In addition to this, illegal 'pirate' radio stations have started to take advantage of this feature - some of these transmitters have the traffic flag set to 'on' constantly, with the obvious effect of switching listeners' radios to the illegal station regularly.

Most people have it turned off!