Slipstreaming?

Traffic technology has this report:

A Japanese team that includes Nissan Motor Co. says that it has successfully tested a system that enables three trucks to be driven automatically in single file, while maintaining a set distance between them. The ‘road-train’ test is part of a project at the New Energy and Industrial Technology Development Organization. The team also includes the Japan Automobile Research Institute, Nihon University, NEC Corp., Mitsubishi Electric Corp., Denso Corp. and the University of Tokyo.
By driving in single file and taking advantage of slipstreams, trucks can reduce air resistance and drag and improve fuel efficiency. In the test, three 25-ton trucks traveled on an 8km test road at an average speed of 80km/h (50mph), keeping the distance between them at 15m. The system, which includes antennas for measuring vehicle distances, control devices for ensuring safe driving, compact cameras for tracking the center line, and laser radars, managed to keep the fluctuation in the distances separating the trucks within 1m.
The team aims to refine the system and realize 4m slipstream driving in around two years, with an eye toward utilizing the technologies for developing a safe and fuel-efficient intelligent transportation system and other applications. The group estimates that keeping the vehicle distance at 4m would cut the three trucks’ fuel usage by 15%, compared with when they are driven separately. The project is also developing a method for estimating carbon dioxide emissions from traffic patterns and the way in which vehicles are driven, as a tool for fighting global warming.
 

A better idea is to get a bigger diesel electric tractor and connect all the trailers into a single train with electric drive and steering.

 Like this, except the trailers need steering by wire so the total rig can travel on normal roads.