Elverson Road, Royal Albert, Gallions Reach and Cutty Sark have not been extended for three-car trains; such extension may be impossible in some cases. Selective door operation is used, with emergency walkways in case a door fails to remain shut. is underground, and both costs and the risk to nearby historic buildings prevent platform extension. The tunnel has an emergency walkway. Additional work beyond that needed to take the three-car trains was also carried out at some stations. This included replacing canopies with more substantial ones along the full platform length. A new has been built east of the former location as nearby curves precluded lengthening. now has a third platform.