Modern cars are much safer in collisions for their occupants than older models, but their extra weight and height mean that they are more likely to kill people in other cars.

A study has found that drivers hit by a car registered from 2000-03 are 46 per cent more likely to die than if hit by a car registered from 1988-91.

The Transport Research Laboratory (TRL), which conducted the study for the Department for Transport, said that the greater risk to other drivers posed by modern cars helped to explain why car occupant deaths had failed to fall significantly in the past eight years.

In 1998, 1,696 car occupants were killed, compared with 1,675 in 2005, a fall of only 1.2 per cent. Over the same period, the annual total for all road deaths fell by 6.4 per cent.

Modern cars have much better safety features, such as multiple air bags, side-impact protection and stronger frames. But these have added weight, the study says, so that the average new car is 20 per cent heavier than one built a decade ago.

Manufacturers have also increased the size of models to satisfy consumer demand for roomier cars with higher performance. Greater acceleration and higher top speed require larger, heavier engines.

For example, the new VW Beetle weighs 1.6 tonnes, double the weight of the rear-engined versions. The modern VW Golf is half a tonne heavier than the 1976 original, 2ft longer and 5in taller. It has a top speed of 146mph compared with 113mph for the Mark 1.

The increase in cars’ average height means that they are more likely to override the stronger parts of another car’s shell in a side impact, increasingly the likelihood of killing occupants.

The study concludes: “Improvements have come at a price: a more modern car tends to be more aggressive than an older car when in collision with another car.”

The average new car scores much higher in crash tests now than in 1998, but the tests measure only how well a car protects its own occupants or pedestrians, not how much damage it can inflict on another car.

Road safety groups called on the car industry yesterday to add an extra crash test to measure the risk that cars pose to occupants of other cars. The Parliamentary Advisory Council for Transport Safety said: “There is a good case for an extra test which will show prospective buyers how much damage a car will do to other cars.”

Andrew Howard, head of road safety at the AA, said that the growing disparity in the size of vehicles was also increasing the severity of crashes because there was now a greater risk of a small car colliding with a larger one.

People carriers and 4x4s, the two largest categories, accounted for only 5.6 per cent of new car sales in 1996 but 12.5 per cent in 2005. Over the same period, small cars also increased their market share, from 27.9 per cent to 31.1 per cent.

The TRL study found that drivers of the smallest cars, such as Ford Fiestas or Rover Metros, are four times as likely to be killed in collisions with other cars as drivers of the largest cars, such as a Ford Galaxy or Mitsubishi Shogun.

Drivers hit by the largest cars are twice as likely to die as those hit by the smallest.

Going green

— The Honda Civic hybrid, which has both a petrol and an electric motor, has been named the greenest car by the Environmental Transport Association

— It emits 109g of carbon dioxide per km, compared with 520g/km for the Lamborghini Diablo, named as the most polluting car

— The five greenest cars:

1. Honda Civic hybrid
2. Vauxhall Corsa 1.3CTDi
3. Toyota Yaris 1.4 D4D Manual
4. Renault Modus 1.2 16V VVT
5. Daihatsu Sirion M300

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