London Security Crackdown Targets Transit

British police are cracking down on security at rail services and airports to thwart terror attacks in the wake of a trio of car bomb attempts over the weekend. No specific intelligence warns of an attack on the subway system or the rail network, but the increased patrols and security checks are a precaution, according to a transport police boss.

Armed patrols have been stepped up at Heathrow and the London City airports following the explosion at the Glasgow airport , and travelers nationwide are no longer allowed to drive directly to the doors of an airport. All travelers have been told to expect delays while the national threat level is at "critical." (More terrorism stories.)