New York City police are determined not to let a “credible” terrorist threat endanger lives and disrupt memorials planned for the 10th anniversary of the 9/11 attacks. As the city ratcheted up its alert to the highest level Friday, police ramped up their presence on subways, bridges, tunnels, and other potential targets. La Guardia, JFK, and Newark airports have also intensified checking procedures for the weekend. Mayor Michael Bloomberg, who took the subway to work this morning, stopped short of giving information of a new threat, but instead said that it was too “outlandish” to be taken seriously. Through the weekend, police will be on duty for an extra four hours and employ bomb-sniffing dogs and radiation detectors.