Many security officials are convinced that the next wave of attacks will come from truck bombs (a favorite of al Qaeda) rather than more airplanes. Police found that Nabil al-Marabh (linked to bin Laden) had attended a truck driving school and had obtained a permit to haul hazardous materials. When police went to arrest him, they found two Arab immigrants who had also attended truck driving schools. Further investigation found 18 Middle Eastern men in Pennsylvania, all of whom had licenses for large trucks and hazardous materials. There are estimated to be 770,000 trucks on the road in the US every day with hazardous materials (gasoline, nuclear waste, chemicals, explosives), including 50,000 gasoline tankers (each of which carries about 10,000 gallons, the fuel load of a trans-continental airliner. Trucking companies have been warned to check everyone who has a hazardous materials permit. Truck driving licenses are fairly easy to get, and in many states a hazardous materials license requires only passing a
multiple choice test of ten questions.