Dust storms have killed hundreds and are a growing problem in parts of the U.S.

The kind of dust storm that suddenly darkened an Illinois highway on Monday and left seven people dead is becoming more common in parts of the U.S., a phenomenon that some researchers say is far worse than generally recognized. The Illinois storm caused a 72-car pileup after high winds whipped dust from recently tilled farms into a cloud that caked the insides of cars. At least 37 people were hospitalized. Such storms often lead to accidents, many of them fatal. There is no definitive tracking of dust storm prevalence nationally,...