Eventually, if multiple vessels stay cloaked and float around, they could potentially collide and that wouldn't be a good thing.
In this case, the potential would be a flat zero.
If you have only two automobiles in existence, odds are that they will collide. After all, they did, in that amusing anecdote about, was it Pennsylvania? But that wasn't due to Pennsylvania being too small for them both. It was about that particular spot being attractive to automobiles.
Take a million billion starships. Spread in the space of the Milky Way, moving randomly, they would never come within sensor range of each other. The odds of a collision would be zero. But take a hundred starships, and have them do what starships actually do - visit planets. Two will collide eventually.
Cityships would
not do what starships do. They would steer clear of planets, of stars, of basically everything. A million billion of them running blind in the Milky Way would
never collide.
By TOS at least some freighters are automated. These slow boats still fly at the speed of the earlier ECS freighters.
We never learn what freighters fly at warp two in TOS exactly. The one from "Friday's Child" was not specified to be automated, at any rate...
Since we see the wreckage of one in Lower Decks, they're not really very big, either.
We actually see wreckage of at least two, both hulls sporting the registry NCC-502. For all we know, the registry applies to a formation, not to an individual hull. And the hulls were associated with rows of containers in that debris field - not just one or two, as in speculative presentations of the
Ptolemy, or even half a dozen pairs, as in ENT, but in a line of dozens. So fairly big in the end...
Crew transport has often been shown by shuttle. One known by name is the Astral Queen. How big and fast she was, is hard to tell but she must have been up to the requirements of the job as the ship was in use in both the TOS and TNG eras.
I'd assume there to exist 1701 ships by that name at any given time!
Whether the ship in "Conscience of the King" was a passenger carrier at all is debatable. Daily's ship there was supposed to do a "pick-up" on the Karidian troupe, but was told to skip that. What sort of a ship can skip a planet on her itinerary? Not a liner, obviously. Not a supply ship delivering needed things. A pleasure cruiser? A tramp (but would one of 'em make a living by stopping for a theater troupe, without arranging for the transfer of at least some goods on the side)? Certainly the
Astral Queen's association with passengers appeared impromptu at best...
The forest ship in the 32nd century Starfleet might be their largest from that era.
Difficult to tell much about sizes yet. But the forest donut did not seem to dwarf the vessels around her.
Timo Saloniemi