DETROIT—After kicking the tires on a shiny new train system, the Motor City has decided to take the cheaper bus instead. This week, the U.S. Department of Transportation and Mayor Dave Bing suddenly abandoned a roughly $600 million plan to build a light-rail line along a key corridor that supporters had insisted would attract new residents and jump-start economic growth. Instead, they proposed a less-expensive plan for a network of express buses to deliver workers from the city to the job-rich suburbs. http://online.wsj.com/article/SB10001424052970204844504577100660265044228.html