The Transportation Security Administration (TSA) has failed to develop and complete comprehensive risk assessments on the trucking and bus industries' vulnerability to terrorism as mandated by both a presidential directive and federal law,the Government Accountability Office (GAO) reports.

"Risk assessment," according to the GAO, "is the process of considering threat, vulnerability, and consequence assessments to determine the likelihood of terrorist attacks and the severity of their impact."

While TSA has conducted risk assessments, the GAO says, it has not done all it could.

Specifically, the GAO criticized TSA for not identifying specific threats to the transportation system as required by Department of Homeland Security policy. Moreover, TSA  has not outlined how it will conduct vulnerability assessments for commercial bus and trucking industries, as required by former President George Bush'sHomeland Security Presidential Directive-7 (HSPD-7). Nor has it conducted consequence assessments for how a terrorist attack involving trucks or buses would reverberate throughout American society, such as its economic impact or public confidence in the industry. The TSA has also failed to complete a report on commercial trucking security as mandated by the 9-11 Commission Act.

"As a result of limitations with its threat, vulnerability, and consequence assessments, TSA cannot be sure that its approach for securing the commercial vehicle sector addresses the highest priority security needs," the report warned.

According to the GAO, the past decade demonstrates the terrorist threat posed by truck and bus bombs. Terrorists have used truck and bus bombs 510 times between 1997 and 2008, the GAO reports.

Truck bombs have been the culprit behind numerous large-scale terrorist attacks against the United States, both domestically and internationally, including the 1995 attack on the Murrah Federal Building in Oklahoma City and the twin attacks on the U.S. embassies in Kenya and Tanzania in 1998. There has also been a surge in truck and bus bombs in Iraq, particularly 2007, the report notes.

“This is the third report this year indicting serious security shortcomings in all modes of the nation’s surface transportation systems," Rep. Bennie G. Thompson (D-MS), chairman of the House Homeland Security Committee, said in a statement responding to the report. "Like rail, transit, and highway infrastructure systems, the security of the nation’s trucking industry is vital to our economy."

The trucking industry numbers over a million companies which help transport 65 percent of the daily freight nationwide. Busing companies carry 775 million passengers a year, more than the airline industry. The GAO says both trucks and buses operate virtually free of restrictions due to the U.S.'s open highway system.

Among the many recommendations the GAO made to TSA to define the risk of terrorist attack to the nation's bus and trucking industries include developing a plan and a time frame for completing risk assessments while formulating performance measures that assess how well federal commercial vehicle security programs are working. The GAO said that DHS, TSA's parent agency, agreed with its recommendations.