The laws that were passed in 30 States and the District of Columbia during 1984-87 varied in their requirements, enforcement provisions, and penalties. Most laws exempt some occupants from coverage even though those occupants have seat belts available for use. Most States had laws that would have applied to more than 90 percent of the motor vehicle occupants killed in their States in the years just before the laws were passed. However, a few States -- those that exempt light truck and van occupants but have many of these vehicles on their roads -- exclude 25 to 40 percent of their occupant population. Only five States had laws that covered all passenger vehicle occupants. Some of the gaps in coverage in the original laws have been subsequently removed through amendments. Table and 7 references. (Author abstract modified)