Just anecdotally, I think the typical Costco trip is alongside trips someone would have taken already.
replyGo to work, take a 5 minute detour to stop by Costco for your prescriptions, gas, and groceries on the way back
It is more like 1 truck delivering 100 single items to 100 homes.
replyWith there typically being a free shipping minimum (or a relatively fixed shipping cost for daily goods), it seems like the benefits of the 1 truck model are likely even greater as customers are explicitly encouraged to group purchases together.
replyMultiple times a week.
replyFor the aforementioned 100 homes, if the 100-items-in-1-truck are needed multiple times per week, then the 100-items-in-100-cars are likely also needed multiple times per week, so the extra CO2 etc would be even worse.
replyNo, not if you're matching the volume of items between the two scenarios.
replyWell, maybe more than one truck.
replyOne truck per delivery service