“Regarding "no Trucks" Signage”

Wasn't sure where to put this, so figured here was my best bet. I have a question regarding the rules behind the no truck signs you see on side streets, and can't seem to find any information on it. The hta doesn't say anything that i could see.

Basically, it was my understanding that those no truck signs reffered to heavy commercial trucks, such as 5 ton trucks or greater (that you need a commercial license to operate). I work for one of the big well known courier companies, and one of my co-workers was telling me the other day he was driving down a side street that has one of those signs (it was a one way, he had a delivery on the next side street which was also one way, going in the opposite direction). He was pulled over by an UC and told residents were complaining about increased traffic because of the pan am games, so they were enforcing the no truck signs and local traffic only in a blitz. He was told he could get a ticket for $110 and 3 points but she gave him a warning and told him he can only go down streets which he can prove he has deliveries for (side streets).

We drive step vans (can par, ups, puralotor, fed ex etc). You don't need a commercial license to drive them, and I wasn't under the impression they were considered "Heavy Trucks". So what defines a heavy truck, as per those signs? And is there an unspoken law that says you can't use a side street unless you live on it?

If anyone can help point me in the right direction for some info, I'd appreciate it. Thanks!

There's more information about this topic in another thread: http://www.ontariohighwaytrafficact.com/post34388.html