def is_motorcycle(df):
    """Return if vehicle is a motorcycle, per NHTSA convention."""
    yr = df['YEAR']
    body = df['BODY_TYP']
    return yr.between(1975, 1981) & body.between(15, 18) | yr.between(1982,
        1990) & body.between(20, 29) | (1991 <= yr) & body.between(80, 89)
