The situation is exacerbated when the screen flashes news of more trouble between the M5/M6 and M6/M54 junctions. Traffic is moving at 10mph on that part of my intended route. These 'real time' reports paint a picture bad enough to merit a change of plan. I leave the motorway, take a quick look at the road atlas and follow a dual-carriageway detour. It takes me to the M6 a few miles north of Wolverhampton, clear of all the trouble.
The system that has made my motoring much easier for the past two months, and 6,000 miles, is called Trafficmaster. Having covered the London area since September 1990, pumping out round-the-clock information about the M25, it was this week extended to more than 1,000 miles of motorways. My enthusiasm is based on an exclusive trial of the new network, bounded by Dover, Portsmouth, the Welsh side of the Severn Bridge, Telford, the M6 north of Stafford, the M1 north of Leicester and the M11 to Cambridge.
Trafficmaster's data comes from hundreds of 'black box' detectors on bridges and gantries about two miles apart. Sensors use infrared technology to measure the speed and volume of traffic in each direction. A microprocessor calculates average speed over a 'rolling' three-minute period. Radio signals alert the control centre in Luton when the average speed drops below 30mph. Then a radio-paging frequency sends the news to the in-car Trafficmaster unit. Information is updated until a 'Reports Clear' message appears on the screen.
Trafficmaster is easy to work. Eight buttons flank a screen measuring about four inches by three. Pressing the right button reveals a clear map that gives an overview of the whole system. Three more dabs of the appropriate button or buttons enable you to focus on a specific area, such as the 25 miles of M4 west of Swindon.
Providing on-the-spot information never more than three minutes old is Trafficmaster's greatest strength. Radio reports, in my experience, are never received until you have been stuck in a jam for ages, and they are not comprehensive. In contrast, the fully portable Trafficmaster unit, which is on my desk as I write this, is providing detailed information about chaos on the M25's western rim, very slow going on the northbound M5 near Worcester and at the M1's junction with the M6. It tells me that clockwise would be the way to tackle the M25 if I were heading down the M1 with Gatwick as my destination.
Problems are often explained by shorthand messages that appear either in a corner of the map or on one of the text pages. This service takes in London itself, so the messages include a warning that the A13 flyover in Canning Town is down to one lane in each direction, due to roadworks.
'The service gives you a chance to choose an alternative route,' says David Martell, whose company, General Logistics, has invested more than pounds 3m in Trafficmaster and is introducing it in the United States. 'You can tell at a glance which way to go round Birmingham and, if you're heading for London, whether the M40 is a better bet than the M1.'
The Confederation of British Industry says traffic congestion costs the nation more than pounds 15bn a year in wasted time and fuel. The figure helps to explain why Trafficmaster's big-name users include British Aerospace, Kodak, Ford, Esso, Barclays Bank, Sainsbury, Virgin Atlantic and ICI. Mr Martell expects the extended coverage to attract between 50 and 100 per cent more customers every week. There are now about 3,000.
I faulted it only once, when heading east along the M54. The screen suddenly indicated traffic down to walking pace on a stretch where only three other vehicles were in sight.
A unit costs pounds 199, but to that must be added pounds 19.50 a month for the information service without which it is useless. Installation takes about two hours, makes no mess - the unit even has a built-in aerial - and costs between pounds 50- pounds 100 (excluding VAT).
Disadvantages are hard to spot. The main one identified during this real-life test is that Trafficmaster attracts a small but not insignificant part of your attention, particularly until the novelty wears off. There is a risk of running into the back of a lorry while reading a message or switching maps to see what is happening in other parts of the country.
When news of a problem ahead hits the screen, it is often tempting to take a quick look at the road atlas while driving. The ideal system would combine traffic information with an element of route guidance.
General Logistics, Luton International Airport, Luton, Beds. LU2 9LU: (0582 484414).