Reduced drag

An automated way of allowing cars to drive much closer to each other in heavy moving traffic, so-called platooning, could cut congestion, save fuel and cut greenhouse gas emissions, according to researchers in India.

As the number of vehicles on the roads in cities and motorways across Europe, North America and the developing world rises, traditional ways of tackling the problem, such as simply building more roads or improving public transport are becoming less and less effective. Automated highway systems are one of the many approaches that have been suggested to tackle the problems.

Driving a lot closer than a safe stopping distance from the vehicle in front is not a sensible option. Yet, according to Debojyoti Mitra and Asis Mazumdar in the Department of Mechanical Engineering at Jadavpur University, Kolkata, India, in heavy traffic, these safe distances mean more tailgate turbulence and increased drag on individual vehicles, which results in lower fuel efficiency.

On the other hand, cars moving in the same direction separated by just a metre or so would reduce drag and so save fuel. And the researchers believe that this could be possible if vehicles were fitted with the appropriate sensors and safety systems.

To test out the effects of such small separations between vehicles, the researchers investigated the drag on platoons of four vehicles in Jadavpur University's vehicle test wind tunnel.

'The leading car in the platoon experiences the highest drag as you would expect but no more than if it were driving alone,' explained Mitra, 'The second car has a much lower drag coefficient than the first car in a two-car platoon. The middle car experiences the lowest drag in a three-car platoon and the third car in the platoon, starting from the front, experiences the least drag in a four-car platoon.'

Reduced drag not only means lower average fuel consumption for a platoon, but also reduces the overall road noise heard by drivers and other road users.