> Apparently this efficiency is due to the reduced spacing at this speed
> as opposed to higher speeds.  It just so happens that maximum fuel
> efficiency is also around 35 MPH, so I jumped to the logical conclusion
> that we could solve two problems at once with a national 30 MPH speed
> limit!  ;-)

This would surely make the Diesel Vanagon owners happy:

"Look, Ma!  I can pass!"
"Yes, dear, but hurry.  That guy on the 10-speed keeps tailgating!"