Congress will return from its summer vacation on September 6. On September 30, federal gasoline and diesel taxes are set to expire. Will renewal be Washington's next major battle? The federal tax on gasoline is 18.4¢ a gallon. On diesel fuel it's 24.4¢ a gallon. That's $100 million a day for the Highway Trust Fund, providing $35 billion a year to road and transit projects run by states nationwide. Keith Laing writes for The Hill, a newspaper widely read by Capitol insiders.