Between 1936 and 1964 — when racial segregation was outlawed by the Civil Rights Act — African American motorists relied on a guide known as “the Green Book” to tell them where they could safely fill their tanks, get a bite to eat and stop for the night. Surely, in the 21st century, advice of that kind is no longer necessary? Ed Pilkington, having made a 900-mile road trip for The Observer through Missouri, suggests otherwise.