Reasons why not 55 MPH
1. It will reduce capacity of highways which have higher speed limit, resulting in more congestion and fuel wastage.
2. Longer travel time will cost more in terms of labor hours.
Better options
1. Use Hybrid vehicles
2. Reduce traffic during peak hours by Telecommuting, Flexible working hours and compressed work week
3. Invest in nuclear energy and alternative fuel research as OIL is a perishable resource, which will last only for about 40 more years.