WASHINGTON, D.C. --- The U.S. average retail price for regular gasoline fell 12.1 cents last week to hit $2.497 per gallon as of Sept. 18, which is 28.9 cents lower than a year ago. Prices fell for the sixth week in a row, reaching the lowest national average price since March 13, 2006, according to the Energy Department's Energy Information Administration (EIA). In its latest weekly report, the EIA said East Coast prices fell 12.6 cents to $2.528 per gallon. The Midwest saw the largest regional price decrease of 12.9 cents to $2.319 per gallon. West Coast prices were still the highest in the nation after falling 10.0 cents to $2.806 per gallon, the lowest price in that region since April 10. California prices were 10.1 cents lower at $2.848 per gallon, only the second week that the state average has been below the $3 mark since April 24, the EIA reported. Retail diesel fuel prices fell by 14.4 cents to reach $2.713 per gallon as of Sept. 18, 1.9 cents lower than last year. This is the fifth week in a row that prices have fallen, the EIA said. Prices dipped throughout the country, with the Rocky Mountains seeing the largest regional decrease of 18.4 cents to $3.052 per gallon. But that's still the highest regional price in the country. West Coast diesel fuel prices fell 12.3 cents to hit $3.014 per gallon.