ASHINGTON

With the arrest of Jose Padilla, our worst fears were confirmed: Al Qaeda was planning to build and detonate a dirty bomb containing nuclear material in an American city. A danger previously relegated to Hollywood screenplays is now a reality.

At the same time, the Senate is in the process of making the most important transportation decision of the new century — whether or not to move 77,000 tons of high-level nuclear waste from power plants nationwide to Yucca Mountain in Nevada. For more than 20 years, debate on the Yucca Mountain project has centered on only half of the issue. The Department of Energy has spent more than $7 billion and 24 years studying the geology of potential repository sites, but only four percent of that has been spent on transportation issues. Yet even despite that spending, Secretary of Energy Spencer Abraham said recently that the department is "just beginning to formulate its preliminary thoughts about a transportation plan." Now, in light of Sept. 11, proceeding with the Yucca Mountain project without a fully secure transportation plan that takes into account terrorism threats is dangerous and irresponsible.

Government officials believe Al Qaeda and other terrorist organizations have sought to purchase uranium and the other necessary tools to make a dirty bomb. According to experts, each truck container of spent nuclear fuel (containers used for rail and barge transport would be bigger) headed for Yucca Mountain would carry more radioactive material than was released by the nuclear bombs used in World War II. If one of these containers were breached, in an accident or a terrorist attack, the results would be catastrophic.

Before Congress makes any decision on where to store this country's nuclear waste, it must first determine whether that waste can be safely transported on our highways, waterways and railways. Congress must require that the Department of Energy conduct a comprehensive risk assessment considering all potential hazards, including terrorist threats. Congress must also demand that the department develop a transportation safety plan that outlines steps to be taken in the event of terrorist acts and accidents. And there must be full-scale testing of the containers to be used for transporting this waste. The transportation plan must be created in an open process that includes input from state and local officials and the public. With our enemy in active pursuit of dirty bombs, our considerations about nuclear waste management have to change.

Secretary Abraham has said there is plenty of time to create a transportation plan before Yucca Mountain begins receiving nuclear waste eight years from now. But safety issues will almost certainly get short shrift if they are not addressed before the repository site is approved. Congress needs to force the Department of Energy to reassess the dangers of transporting high-level nuclear waste and develop a secure plan before proceeding with the Yucca Mountain project.

Jim Hall, a member of the National Academy of Engineering's Committee on Combating Terrorism, was chairman of the National Transportation Safety Board from 1994 to 2001.