The recommendation from the National Transportation Safety Board came after it investigated five fires this year involving the Silverliner IV passenger railcars used by the Southeastern Pennsylvania Transportation Authority, or SEPTA. All five fires forced everyone aboard to evacuate — in one case, as many as 350 passengers — with a few minor injuries reported. One railcar was involved in two of the fires, and two other railcars were destroyed, the NTSB said. SEPTA is one of the nation’s largest mass transit agencies, carrying 800,000 daily riders on buses, trolleys and rail. Still, it said the replacements are “long-overdue investments” and “can no longer be delayed.”It put the price tag at nearly $1 billion to replace its 230 Silverliner IV cars built by General Electric in the 1970s.