The “bubble” roof was part of a £44 million (approximately $60 million in U.S. funds) upgrade project completed in October 2015. It consists of more than 400 translucent ETFE panels supported by 15 giant steel ribs. The station’s 8,500-square-meter roof arcs over its new railway concourse, linking in with the station’s original Grade II-listed buildings. Witnesses say the roof was visibly damaged at least a week prior to the accident. There is no determination at this point as to the cause of the buckling.