Truck bombs (search) aren't a new terror weapon of choice, but since they're fairly easy to make, deadly and extremely destructive, they're certainly one of the most effective.
"It is the definite, definite weapon of the next attack," said Juval Aviv (search), president and CEO of Interfor, Inc., an international corporate intelligence and investigations firm. "This is the easiest one to do — this is a weapon they've been using for 35 years all over the world and is extremely successful."
Walter Purdy, a vice president of the Terrorism Research Center, said the risk of such an attack was huge. "Terrorists love to use truck bombs. ... The bigger the truck, the more explosives they can get into the things."
The United States has spent more than $1 billion on defense measures to guard against car and truck bombs, which proved deadly in attacks like those in Beirut in 1983, the first World Trade Center bombing and at U.N. headquarters in Baghdad last August.
So with the recent intelligence information leading authorities to raise the terror alert (search) level for financial centers in New York City, northern New Jersey and Washington, D.C., those areas are going on the offensive. More cement jersey barriers are around Manhattan buildings like Grand Central Station and the Federal Reserve Building, while wider perimeters have been installed around such potential targets.
The New York Police Department, for example, is also conducting random spot checks of trucks, although a spokeswoman said she couldn't give specifics on where and when these checks were taking place.
Aviv, who served in Israel's elite intelligence unit and has worked security for El Al Airlines and consulted with various U.S. agencies and corporations, said the only sure way to prevent a truck bomb in a city like the Big Apple is to inspect every truck before it crosses any bridge or goes through any tunnel into the city.
"More control has to be on the outside of the city before they enter the city," Aviv said. "Right now, what we do are spot checks, we block roads somewhere … but what terrorists are notorious for doing — they drive a truck bomb and in front of the truck, drive a regular truck with a radio." That way, Aviv said, a checkpoint can be reported and the truck bomb driver can try another route.
Former Assistant FBI Director Danny Coulson said it's not impossible to stop every truck even though some may believe it to be a "hopeless task."
"The key to it is getting these guys before they get to the plot," Coulson said. "Intelligence plays a big role in telling where they want to go, then you just try to keep them [trucks] away from there."
Tankers, SUVs and Pickups
Purdy agreed that spot checks, while somewhat effective, aren’t a sure bet. A better plan of attack, he said, is to garner better intelligence pointing to specific vehicles that may be used and/or specific locations that may be targeted and home in on those.
"When you stop to think about how many trucks there are in the United States … even if you knew someone was contemplating doing this, you could really cut off all commerce if you stopped every single truck, really," he said.
Vigilance is the key deterrent, however, experts said.
"I think we've learned a lot since 9/11 and we've done a lot of work; I think it shows the system is working," said Michael Bouchard, assistant director of the Bureau of Alcohol, Tobacco and Firearms. "I think all of us as Americans, we're all paying more attention to what's going on around us."
If enough precautions aren't taken, however, a truck bomb detonated in a crowded area such as lower Manhattan could be devastating.
"You kind of get a bounce effect when you have an explosion from a truck bomb" in an area where buildings are close together, Purdy said. "Some of these individuals are skillful enough so they can factor those things in. … If you can get a truck bomb in downtown lower Manhattan … with 4,000 pounds of explosives, you're going to basically take out that 200-year-old building."
One problem with truck inspections, however, is that it doesn't take an 18-wheeler to deliver a deadly weapon.
In the May 2003 attacks in Riyadh, Saudi Arabia, for example, an SUV, car and pickup truck loaded with 500 pounds of RDX — a higher grade military-type explosive — were used. A cement truck was used in the U.N. bombing in Baghdad.
"It's not just one particular type of truck," Purdy said. "Just stealing a tanker filled with fuel and driving into a crowded downtown, metro-type area with large groups of people and having an explosion set that off, that will also have the type of effect these people are looking for."
'It's Almost A Chess Game'
Another step being taken to combat the threat is more oversight of ammonium nitrate (search) sales. More than 1.5 million tons of the fertilizer ingredient were sold in the United States last year. It's a favorite for terrorists like Timothy McVeigh (search), who was convicted in the 1995 Oklahoma City bombings. It was also used in the 1993 World Trade Center bombing.
"These fertilizer bombs are very, very effective … it basically picks the buildings up and drops it," Coulson said.
On July 30, the FBI and the Department of Homeland Security issued a bulletin entitled, "Potential Threat to Homeland Using Heavy Transport Vehicles," to state agencies and other organizations.
"There have been multiple suspicious incidents over the last six months that heighten concern over the potential terrorist acquisition of large trucks and commercial buses," the bulletin said.
There are currently no federal laws regulating the purchases of this material. Only South Carolina and Nevada require ammonium nitrate buyers to show ID and sellers to keep records of any purchases of the fertilizer. In 1998, the National Academy of Sciences recommended that Congress pass legislation to tighten the sale of this product, but nothing happened.
Now with the most recent alerts, New York Sen. Charles Schumer in the fall will introduce a three-point plan to prevent future attacks: ID checks at point of sale, hotline background checks on all bulk purchases, and "taggant" identifiers placed in all ammonium nitrate. Taggants let law enforcement identify sources of bomb materials and could serve as a deterrent.
"Al Qaeda’s standard M.O. has never been to use fancy weapons but rather to use the simplest things — like small knives and box-cutters to commandeer a jetliner — as lethal weapons against us," Schumer said in a statement. "We know Al Qaeda uses the Internet, and there are dozens of sites there describing how to make a truck bomb out of fertilizer. In light of this reality, the least we could do is take some commonsense, simple steps to know who is buying this explosive and where it is going."
But one question left unanswered is whether protective measures being taken to prevent such attacks will deter or thwart any terrorist plot.
"So often these terrorists are not deterred, it's almost a chess game, you move one piece, they move one piece," Purdy said. But the more security there is, the longer it takes the terrorists to hatch an effective plan, giving law enforcement even more time to botch it.
"Every time they have to go back … they might have spent six months planning that so now all that planning and money and effort just went down the tubes," he said. "Now they almost have to back and start again and say, 'OK, where do we get a fire truck? Where do we get a limousine?'"
FOX News' Jeff Goldblatt contributed to this report.