A driverless car developed by Oxford University  spin-out Oxbotica

Driverless cars may increase congestion, at least temporarily

Image credit: Oxbotica

Driverless cars, touted as a means to decrease congestion and increase safety, may have the opposite effect, at least temporarily, according to a new study.

The introduction of autonomous vehicles will present many challenges. At the beginning, the super-intelligent driverless cars will mingle with old-school vehicles steered by human drivers and will have to take an extremely cautious approach in order to ensure safety. This cautious approach is likely to result in increased travel times and delays until the proportion of autonomous cars grows beyond a certain threshold that will allow more assertive behaviour on the roads.

A report by the UK Department for Transport (DfT) found that in a situation where 25 per cent of cars on the roads are driverless and the rest driver-dependent, delays might increase by almost 1 per cent.

The report estimates that the tipping point will come when about 50 per cent of vehicles rely on automated connected technology, which will allow decreasing gaps between cars.

At 50 per cent penetration, delays will decrease by 7 per cent. Once 75 per cent of the overall fleet is driverless, the delays will be reduced by 17 per cent. When all vehicles are autonomous, the delays will be cut by 40 per cent.

The greatest benefits are expected in congested networks with high density of traffic, where autonomous cars will be able to operate more smoothly. These, mostly urban areas, are actually expected to see benefits already with low penetration of driverless vehicles. With a quarter of cars autonomous, city traffic may see a 12 per cent improvement in congestion.

“There’s a prize to be had in terms of swifter, safer journeys, but the transition to that world will be challenging,” said Steve Gooding, director of motoring research charity the RAC Foundation.

“There are around 32 million conventional cars on the UK’s roads. As driverless cars come in, traffic flow could initially get worse rather than better, potentially for many years. Much will depend on how an autonomous car’s parameters are set and just how defensively these vehicles will be programmed to drive.”

The DfT study used computer modelling to simulate various parts of the road network including a section of a motorway.

“This exciting and extensive study shows that driverless cars could vastly improve the flow of traffic in our towns and cities, offering huge benefits to motorists including reduced delays and more reliable journey times,” said transport minister John Hayes.

The DfT said the report paves the way for further trials and research into driverless vehicles to ensure their development is safe and beneficial for all.

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