What singer was inducted into the Rock and Roll Hall of Fame in April 2014 and did guest vocals on the Old Train album?
Old Train:  The record is a mixture of progressive, traditional bluegrass and folk material and also features guest musicians as Ricky Skaggs on violin or Linda Ronstadt on vocals. Linda Ronstadt:  She was inducted into the Rock and Roll Hall of Fame in April 2014.
Linda Ronstadt