According to the new standards of fuel efficiency adopted by the united states, average fuel efficiency for all passenger vehicles must be increase to by the year 2020.

35 MPH.

Explanation:

As per the new standards released or fuel-efficiency approved by the United States, the average parameter for fuel efficiency has been increased to '35 MPH' until 2020 for all the commuters. The decision was made with a view to set limitations on the average fuel consumed as per the increasing demands of the consumers but still restricting the use up to '35 MPH in order to enhance the average fuel efficiency of the vehicles that would not only save the consumer's affluence but also help conserve the resources by using it efficiently.