“The idea is to use a pickup truck as a mowing machine, not to mow grass but mow down the enemies of Allah,” said a 2010 magazine called Inspire, allegedly written by members of al-Qaida in the Arabian Peninsula. “To achieve maximum carnage, you need to pick up as much speed as you can while still retaining good control of your vehicle in order to maximize your inertia and be able to strike as many people as possible in your first run.”…

Because the danger from vehicles is well known, federal and local law enforcement have protocols to protect large public events from trucks, said John Halinski, a former deputy administrator at the U.S. Transportation Security Administration who is now a security consultant.

“When you have events like that, you should barricade off the streets,” Halinski said. Photos of the carnage in Nice appear to show that precaution wasn’t taken, he said.