An early morning fatal train strike that caused a four-hour suspension of service Friday on the Ronkonkoma Branch of the Long Island Rail Road is being investigated as "a possible suicide," railroad spokesman Aaron Donovan said.

The incident occurred at the Fifth Avenue grade-level crossing on the Brentwood-North Bay Shore border at 5:50 a.m. Donovan said the victim was an adult male, but said the victim's identity was not being released pending family notification.

Railroad officials did not say why the incident was being investigated as a suicide.

Service on the branch was restored, with residual delays of up to 20 minutes, about 9:15 a.m. Friday, officials said.

By 10:45 a.m., Donovan said, the railroad was operating on schedule -- without delays.

Earlier, Donovan said the service suspension covered all scheduled trains between Ronkonkoma and Hicksville.

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The railroad had urged riders to use the Babylon Branch as an alternative route for their morning commutes. At 8 a.m., the railroad said it had restored service eastbound from Ronkonkoma -- with trains making all local stops, departing Ronkonkoma on the hour and half-hour. However, eastbound service remained suspended at that time east of Farmingdale.

The fatality involved the 5:29 a.m. train from Ronkonkoma that was due to arrive in Penn Station at 6:38 a.m.

Donovan said the scene is two crossings east of the Deer Park station and that the train was being held there.

An assortment of other issues were also affecting railroad service Friday morning. Equipment trouble forced the cancellation of the 6:27 a.m. train from Port Washington. Signal trouble caused the 6:47 a.m. train from Atlantic Terminal to Long Beach to operate 22 minutes late -- after being delayed at Jamaica.

Equipment trouble forced the cancellation of the 7:49 a.m. train from Far Rockaway to Penn Station and delays to subsequent trains, officials said.

Planned track work was affecting service to customers on the Port Jefferson Branch, where buses were being used to replace trains between Huntington and Port Jefferson.

Officials urged branch customers to pick up the Port Jefferson Branch Timetable dated June 24 through Aug. 9 for specific train and bus information. Westbound customers using stations between Port Jefferson and Greenlawn were to board buses up to 24 minutes earlier than normal scheduled train times. Officials said customers could transfer to westbound trains at Huntington.

Eastbound, customers were boarding buses at Huntington for transit to stations between Greenlawn and Port Jefferson.

Meanwhile, all Babylon Branch westbound trains were ordered to stop at Jamaica on Friday to accommodate customers from the Ronkonkoma Branch, the railroad said.

At least one Babylon Branch train, the 8:35 a.m. train from Babylon to Penn Station, was canceled due to an equipment shortage as a result of the fatal strike and service suspension.

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The railroad said customers were accommodated by the next westbound train.