This is one of the safest of the advanced hypermiling techniques.  It takes advantage of aerodynamic situations created when a hypermiler like us goes at or below posted speed limits and the normal folk go around you to zoom off to their destinations.

As they go around you, they create a low pressure zone across the entire roadway called the traffic-side draft.  When coasting with the engine off, this low pressure area will give you a 15 to 20 second boost as it sucks you along.

So in a nutshell, this is how you do this technique:

1. On the highway, stay on the rightmost lane.
2. Follow the posted speed limits. Halfway between minimum and maximum posted limits work best.
3. Start to coast when the opportunity presents itself (I personally coast with the engine on by putting the car in neutral, others turn the engine off).
4. Enjoy the benefits of the traffic-side drift as the cars zoom around you.

This is the only publicly recommended technique by Wayne Gerdes the father of hypermiling.