Costs
This has nothing to do with savings and all to do with reducing the carbon footprint of air transportation. Well thought out, this could lead to the largest "green" modernization of our airports as we know them.
Investment??? $8.00 - $50 per one way based on weight and miles flown. Who pays for it?? The people who use the aviation system, not the tax payers.
Funny how many will challenge a "green" offset which will fund facilities and services which will have substantial long term benefits; but, not lift a brow at the aditional concession fees charged by many airport services to build new facilities; i.e. rental car companies at SFO, DEN, DFW, etx.