Tighter Fuel Efficiency Standards: Why isnt that on the agenda?

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I heard that ya there are some fuel efficiency standards. .. What i dont get is why that isnt being discussed further?

As if governemnt regulation set the min engin efficiency standards for all vehicles on the public roads to be set higher. .. Doesnt that naturally work towards building more efficient vehicles.

http://www.nhtsa.dot.gov/portal/site/nhtsa/menuitem.d0b5a45b55bfbe582f57529cdba046a0/

... i'll write more on this later :)