The most frequently asked question in platooning debates is: how close should the vehicles get to each other? Aerodynamically, the answer seems simple: as distance shortens, the wake region the following vehicle travels in strengthens and the drag gain grows. In real operation, however, the equation is far more layered.
Two Sides of Distance
At very short intervals, the following vehicle's engine cooling airflow decreases, sensors' field of view narrows, and the safety margin in braking scenarios thins. As the interval lengthens these risks recede; but it also becomes easier for other vehicles to cut in, and every break-up zeroes the convoy's gain until it re-forms. In practice, therefore, the target is not a single ideal figure but a dynamic distance band managed according to road, traffic and weather conditions.
Other Variables Affecting the Gain
- Cruising speed: because aerodynamic drag grows with the square of speed, the gain is meaningful at high speed
- Convoy length: middle vehicles take the largest share of the two-way effect
- Vehicle geometry: box, tanker and lowbed combinations produce different wake profiles
- Crosswind: shifts the wake region sideways, eroding the gain
The honest summary is this: the platooning gain is real and measurable, but there is no catalogue figure. The lesson the aerodynamics literature gives for on-vehicle equipment holds here too: the decision must rest on data gathered under conditions resembling your own route and speed profile.
References
- Van Raemdonck, G. M. R. & Urila, I. (2019). A Study in Options to Improve Aerodynamic Profile of Heavy-Duty Vehicles in Europe. Sustainability, 11(19), 5519. DOI: 10.3390/su11195519