For the first time in a month, average Virginia gas prices have fallen below $4.00 a gallon — but experts say there is no way to know for sure how far or for how long that downward trend might continue, especially with normally-busy summer travel season ahead. The statewide average is $3.98 a gallon for regular, and in Roanoke, it’s $3.89. That’s down nine cents in a week and 29 cents from one month ago. Experts say there is one reason most in play for that decrease, as WFIR’s Evan Jones reports: