Rail passengers are facing a fourth consecutive day of travel disruption on Friday as RMT union members launch a fresh 48-hour walkout.The strike at Network Rail and 14 train operators means only around 20% of normal services will run with trains starting later and finishing earlier.The walkout is again hitting key TfL services in London with severe delays to Elizabeth Line trains running between Paddington and Reading and Liverpool Street and Shenfield.The London Overground and Circle line are also severely affected while the Bakerloo line is part suspended.The action follows a stoppage on Thursday by train drivers in the Aslef union which caused widespread disruption.