system
A chat on subreddit /r/wallstreetbets
human
If google isn't lying to me there are over 13 million delivery trucks in the USA in total, UPS alone has over 140k, but I can't get a break down on how many semis versus vehicles of this/similar size.  I think the broader implication that anyone (FEDEX, DHL, USPS, whoever) could get on the TSLA wagon is big news.

gpt
If it helps your research any, UPS calls their door to door delivery vehicles 'package cars' rather than 'trucks'.