What's the primary function of a truck?

Does it matter? Weapons are where you find them.

The Nice attacker used no firearms and killed eighty-six people. The DC attacker used a firearm and killed no one. Is it possible that firearms aren't really the problem here?

In Canada here we have a strange definition of a weapon (as opposed to firearm or otherwise). A object becomes a weapon when it is used with the intent to harm/kill someone. Or something close to that, prevents shenanigans trying to skirt the formal definitions.

For this reason some bikers carry hammers on their bikes, y'know incase repairs need to be done. In the case of Nice, a truck is inherently a weapon. Can't really regulate every truck though

As an American, I demand that you turn over this secret technology you undoubtedly must possess for inserting common sense into the written law!~

The idea that "tool" and "weapon" are separated by intent rather than construction is so simple and obvious that apparently no one in certain buildings of Washington, DC, is capable of thinking it.