Trucks are parked during the Great American Trucking Show in Dallas last August. Prices of diesel fuel are down 29% over the past nine weeks. Bloomberg News Diesel prices in the U.S. declined for a ninth straight week, their longest losing streak on record, as continued moderate weather in the Northeast kept heating-oil demand subdued. Front-month futures for ultralow-sulfur diesel, which are also used as a proxy for heating oil, have dropped in recent months alongside plummeting crude-oil prices. Crude oil is refined into diesel, among other fuels. While diesel is mostly used as a transportation fuel, cold-weather demand for heating oil can cause diesel futures to spike in the winter. Prices rose 6.6% in January 2014 as frigid temperatures spread across much of the nation. This year, temperatures have been mild and refinery production is high. Consumers in the Northeast, where heating-oil use is most common, are […]