High gasoline prices in recent years helped give public-transit agencies across the U.S. their best ridership numbers in half a century. Now, falling prices run the risk of putting those gains in reverse. The swift drop in gas prices, to less than $2 a gallon in much of the nation, already appears to be encouraging Americans to drive more. Miles driven increased 3% in October from a year earlier,the largest year-over-year gain since 2006,and advanced 1.1% in November, according to the U. S. Federal Highway Administration. It is too soon to say whether those Americans who are driving more are forgoing public transit, but an extended run of low gas prices could change the cost calculus for transit riders. And a lasting shift could boost pressure on governments from Seattle to Salt Lake City to Cleveland to re-evaluate their expansion plans for buses, subways and trains amid limited […]