Motoring / Road Test: A car that goes with the flow: Roger Bell takes an ecological trip in the VW Ecomatic, which is coasting into first place as the most environmentally friendly car

The engine of VW's revolutionary Golf Ecomatic works like a cyclist's legs - only when needed. Just as a bicycle freewheels when you stop pedalling, so the eco-friendly Golf, powered by a frugal 1.9-litre diesel, slips into neutral and coasts with a dead engine when you release the accelerator. Pressing it again causes the cat-cleaned motor to start immediately, and the clutch seamlessly to engage.

The Ecomatic system, under development for 10 years, is VW's answer to urban pollution. The makers claim an average cut in fuel consumption, and therefore of 'greenhouse' carbon dioxide, of 22 per cent. Other emissions are reduced by up to 36 per cent. As well as being the world's most environmentally friendly car, and cheap to run (though not to buy), the Ecomatic Golf is easy to drive.

There is nothing special about the engine, clutch and gearbox; all are standard Golf items. It is the Ecomatic's control systems and ancillaries that add complexity, cost and weight. When right-hand-drive models go on sale here in June, prices are expected to be about pounds 900 higher than for a comparable Golf diesel with normal transmission.

Although there are only two pedals - go and stop, as in an automatic - there is a conventional gear lever. To start the clattery non-turbo diesel engine, you turn a key; to drive away, you engage first gear and press the accelerator. Moving off and changing gear are easier without the encumbrance of a clutch pedal. If the car has slowed right down while coasting, a flashing dashboard light reminds you to change to a lower gear before pulling away again. The engine will not cut out while it is idling after a cold start and, to facilitate car-park manoeuvring, switch-off is also delayed for five seconds in first gear.

From second through to fifth, however, the transmission is programmed to slip into neutral - and the engine to stop - within a second or so of the accelerator being released. You coast up to traffic lights with nothing more than tyre swish and wind whoosh to disturb the peace. When the car is stationary, there is no noise, nor any pollution: no engine, no exhaust.

At first, the absence of engine braking - quite strong in a normal car in low gear - is disconcerting. For steep descents, however, it can be restored as a safety measure by pressing an override switch that prevents coasting. Although the car's brakes are more than adequate on their own to cope with normal duties, pad and lining wear is increased.

The Ecomatic works well in city traffic, where the engine might be switched off for as much as 60 per cent of the time. VW talks of an urban-cycle fuel consumption of 61.4 mpg, compared with 43.5mpg for a normal Golf diesel. Fears that the engine will not start again instantly when the lights turn green are quickly allayed: the test car's diesel always fired immediately with a dab on the throttle.

Despite its automatic engagement, the clutch's action was sometimes a bit abrupt, and initial acceleration was even more sluggish than that of a normal Golf diesel - the extra weight blunts performance. The jerkiness also made close-quarter manoeuvring in reverse tricky. Clutch adjustment, it seems, is critical.

To coast an ordinary car in neutral with a dead engine would be dangerous. Apart from the risk of activating the steering lock, the brakes and steering would be deprived of power assistance. With the ignition off, much of the electrical system would be out of action, too. The Ecomatic overcomes these problems with special systems: the steering is assisted electrically, not by the engine, and an electric pump tops up the brake-servo. Another pump circulates hot water to the heater when the engine is stationary. To cope with all these extra electrical loads, the Ecomatic has a high-capacity alternator, and a massive main battery supplemented by an auxiliary for starting.

Although the Ecomatic is a perfectly acceptable long-distance car, it offers little or no economy benefits beyond the city limits; fuel consumption is actually poorer than a normal Golf diesel's on open roads, according to one independent test. VW concedes as much by promoting the Ecomatic as a second car for short hauls, or as a municipal runabout.

As a cost-cutting economy car, the Ecomatic has its drawbacks: for many, the savings in fuel could not outweigh the premium on the purchase price. As an ecological car, however, it has no equal.

SPECIFICATIONS

VW Golf Ecomatic, approximately pounds 11,000

Engine: 1.9-litre, four-cylinder, eight-valve diesel; 64bhp at 4,400rpm. Transmission: five-speed manual gearbox, automatic clutch, front-wheel drive. Performance: 0-60mph in 17.5 seconds, top speed 97mph. Fuel consumption: 45-65mpg derv.