Integrating four major aerodynamic features can save about 10% of heavy trucks’ fuel: a nearly sealed tractor-trailer gap, full skirting of the tractor and trailer, a rear drag reducing device, and
optimized cab shape with minimal aerodynamic discontinuities. Tractors and trailers are often owned and usually made by different companies, however, so integrating aerodynamic improvements between tractor and trailer will require greater collaboration.
Bockholt, Wendy, and Matthew Kromer. 2009. Assessment of Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles. TIAX LLC.