I drove 228 highway miles on the Mass pike, NY Thruway at 55-60 MPH and I got over 43 MPG.
Most people are driving just as fast as ever, you can easily save 15% driving slower.

These are my calculations.  The return trip is amazing.  I coasted down a few hills coming out of the Berkshires.
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1.  Hess Station Smithfield, Rt 44, RI  to Hess Station, Oneonta NY
2008/07/12  55-60 MPH
227.8 Miles  5.218 gallons   43.656 MPG
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2.  Hess Station, Oneonta NY  to Hess Station Smithfield Rt 44, RI
2008/07/14  55-60 MPH
227.3 Miles  4.5 gallons  50.511 MPG

Tony Ricci
Rhode Island

Ed note: EPA estimates for Tony's vehicle range from 28 to 33 MPG highway (22-25 city).