BEVERLY – North Shore riders on the Newburyport/Rockport line may be facing more trouble getting to and from Boston.For the fourth time in less than a month, the troublesome rail bridge over the North River acted up again Tuesday.Commuters trains were running over the Beverly-Salem bridge, but at reduced speeds with passengers told to expect delays of 10-15 minutes. The 6:30 a.m. inbound train was canceled.The swing bridge over the Danvers River has been shut down three times since Dec. 21, when it was struck by a barge. A gearbox on the bridge was replaced after a mechanical failure on Jan. 2.The bridge had to close again last Thursday when a problem developed with the new equipment.Material from The Associated Press was used in this report.