It took five hours to rescue 24 people stranded on a roller coaster in Maryland yesterday. Prince George's County fire officials said 17 adults and seven children were stuck at the top of the Joker's Jinx roller coaster at Six Flags America in Maryland. An assistant fire chief said the riders were sitting upright. A few had cramps, back pain, and dehydration, but there were no major injuries. A Six Flags America spokesman said in a statement that it is not yet clear what caused the ride to stop but that it has a computerized safety system that "performed as it is designed to." At another Six Flags earlier this month, a roller coaster stopped dead near its peak.