An automated way of allowing cars to drive much closer to each other in heavy moving traffic—“platooning”—could cut congestion and reduce fuel consumption and emissions by reducing aerodynamic drag, according to researchers from Jadavpur University in Kolkata, India. Their work is described in a paper in the current issue of the International Journal of the Environment and Pollution.
Traffic congestion is a growing problem across the globe and is becoming acute in areas of rapid economic growth, such as China and India. Congestion exacerbates the already growing problems of rising fuel consumption and emissions of criteria pollutants and greenhouse gases.
Automated highway systems are one of the approaches being explored to mitigate congestion, and platooning—the synchronized movement of two or more vehicles as a unit, travelling at the same speed with relatively small inter-vehicle spacing—is one of the possible aspects of such an automated system.
Debojyoti Mitra and Asis Mazumdar at Jadavpur University assessed drag on a maximum four-vehicle platoon model inside the university’s wind tunnel using several car and bus models as platoon members. Intra-platoon spacing was 2/5th the length of the vehicle—e.g., cars 5m in length were spaced 2m apart. Air velocity was 23 m/sec (82.8 km/h or 51 mph).
They found that the platooning of vehicles at close spacing reduces the drag coefficients of all platoon members, regardless of the vehicle’s shape. The higher the number of vehicles in the platoon, the lower the drag coefficient.
The leading car in the platoon experiences the highest drag as you would expect but no more than if it were driving alone. 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.—Debojyoti Mitra
|Drag coefficients (CD) in a four-vehicle platoon|
|Car platoon||Bus platoon|
To make such an approach practical from a safety point of view, sensors and safety controls that allow vehicles to drive at such a small separation would be required.
Mitra, D. and Mazumdar, A. (2007) ‘Pollution control by reduction of drag on cars and buses through platooning’, Int. J. Environment and Pollution, Vol. 30, No. 1, pp. 90–96.