Well, if that visor works anything like the artist illustration below, then apparently the air gets squeezed out to the sides.
Model 587 Features & Specification | Peterbilt On Highway Trucks | Peterbilt Motors Compan
And, if the front wheel fairings taper at the aft, there should be a small footprint there. A big bonus would be venting the wheel wells at that location like a race car.
As much as I want to get nit-picky about this design, I am hopeful they did their homework and it is not just a styling exercise.
http://ecomodder.com/forum/showthrea...-26678-59.html
In anycase this is a fresh looking approach.
Some well rounded edges/corners on that hood would have helped though.