Trucks – especially tankers and hazmat rigs – are receiving more vigilant scrutiny at the border after Homeland Security Secretary Tom Ridge raised the national terror alert to orange – the second-highest level on a five-point scale.

The action comes on the heels of last week’s warning by the Department of Homeland Security that Lake Erie-area trucking companies should watch out for what the agency said was possible terrorist activity involving trucks in the region.

Meanwhile, truck checkpoints throughout several states were heightened at bridges and highways, and many weigh stations across the nation remained open for 24-hour mandatory truck inspections.

For example, Ohio Gov. Bob Taft has called on the Ohio Highway Patrol to open truck weigh stations for 24-hour inspections in Dayton, Columbus, Cincinnati, Akron, Cleveland and Youngstown – and all trucks must stop.

In California, on the southbound approach to the Golden Gate Bridge and on northbound Highway 101 near Candlestick Park, the California Highway Patrol set up mandatory truck stops and checked the drivers and the manifests of trucks going in and out of the Port of Oakland. CHP teams focused on hazardous materials loads.

Inspections have increased at all 301 entry points along the nation's borders, and holiday leaves for Customs and Border Patrol agents were canceled, said Robert Bonner, commissioner of the Bureau of Customs and Border Protection.

"We are increasing our scrutiny of both people and vehicles coming into the United States," Bonner told The Associated Press. A particular focus, he said, is the screening of cargo containers at seaports.

Across the country, security was strengthened for key bridges, tunnels, seaports and landmarks, such as the Gateway Arch in St. Louis, as well as at nuclear and chemical facilities and other installations that might be vulnerable to attack, The AP reported.

Ridge said threat indicators were "perhaps greater now than at any point" since September 11, 2001. In a Sunday conference call with the nation's governors, Ridge said the terror sources were credible, and there were specific references to suicide missions and use of weapons of mass destruction.