The problem isn't trucks -- obviously, it's hugely more efficient for a single truck+driver to deliver 100's of packages in a single day than for 100's of individual people to spend an hour each going to/from a store, and even worse for congestion if even more than a few are taking individual vehicles. The problem is parking. And the solution is obvious: multiple truck-length parking spaces along each and every block…
I thought we were supposed to be designing cities for people and not vehicles. Isn't the answer for everyone to bike with their bike trailer to a central warehouse and collect their own packages?
Delivery reduces traffic by having 1 truck drop off 100 packages instead of 100 people picking up 1 package.