The American economy edged further into the slow lane last quarter, as consumers took their foot off the gas and businesses pulled back. The 0.5 percent growth rate in the first three months of 2016, which the Commerce Department reported on Thursday, underscores a downshift that began late last year. While consumers eased up slightly on spending, business investment fell sharply, stung by lower outlays on equipment and infrastructure like factories and drilling rigs. The business pullback, driven in large part by the ongoing woes in the oil industry, shaved more than half a percentage point off the growth rate. Additional bumps in the road came from a weaker trade picture and the slow movement of big inventories accumulated last year.