The alert says al Qaeda operatives may attack targets with fuel trucks, though officials stress that it is based on uncorroborated intelligence.
Nonetheless, says Larsen, there is cause for some concern.
"For years," Larsen
"(But) this (latest warning contains) very specific information: three cities, the type of weapon, the type of attack.
"This gives police chiefs something to do. And I think, if you're driving a tanker truck in one of those three cities today, there's a high probability you might get pulled over and have police check your license and registration and whatever."
Larsen says the main concern is liquefied natural gas, known as LNG, which is so explosive it can engulf an entire building if a truck carrying it crashes into one.
Larsen says LNG poses a significantly more ominous threat than gasoline: "A big truck of gasoline might be more dangerous to you when you go to the gas pump to pay for it."
And Larsen isn't high on the idea that all people driving trucks with hazardous cargo be fingerprinted.
"On the surface," he says, "it sounded reasonable when they first started it. But there are 2.7 million people with permits to carry hazardous cargo. The TSA (Transportation Security Administration) says it will cost about $100 each to fingerprint them and check them against known terrorists. That's a quarter of a billion dollars.
"The Transportation Department tells us what (qualifies as) hazardous cargo. Here's who we're fingerprinting: people who carry paint, fingernail polish remover, Coke syrup and, my favorite, Listerine. So, it's not a very well-focused program, and I don't think it's the best way to be spending our limited resources.