RONKONKOMA - Some Long Island Rail Road (LIRR) commuters are concerned tonight after learning that Osama bin Laden was apparently planning to target U.S. mass transit systems.

Government officials say a plot to attack trains on the 10th anniversary of Sept. 11 was laid out in handwritten notes that were uncovered in bin Laden's compound in Pakistan.

Officials say one idea outlined in the notes was to derail a train so that it would fall off a bridge.

"Mass transit is the Number 1 target of al-Qaida," says Rep. Peter King (R-Seaford), the chairman of the House Homeland Security Committee.

The confiscated materials taken during the U.S. raid that killed bin Laden revealed the rail attack had been in the works since February of last year.

While officials say the plot was only in the initial planning stages, an FBI alert was issued anyway.

Since last Sunday, security has been stepped up throughout the LIRR system and at Penn Station. In a statement, the Metropolitan Transportation Authority said that it serves as another reminder that the city's transit system "remains a top target."

King says while the new threats may not have been past the tentative stage, commuters must still remain alert.VIDEO: President Obama announces Osama bin Laden's death