By making the roads single-direction and roads owning the movement, I think it’s been made equivalent to a conveyer belt… which means factorio’s conveyor belt optimizations might be relevant.
Eg storing the delta between items rather than tracking position directly, because the distance between cars is static for the length of the road, except during compression, insertion or removal of a car
The distance is not static because of cars stopping for one another.
That’s the compression, same story in factorio. Before/after compression it’s static, so you can avoid having to update any value.
The main difference from factorio belts I think is actually in the insertion — if there’s no room in the belt, insertion is blocked; whereas I’d expect a car to “slip in”.
But I think you can still say that maintains the property that a compressed belt will always be compressed, excepting insert/removal; and insertion/removal just requires updating a static number of deltas (2, in the middle of the line, 1 at the end of it)
And Factorio belts can have stuff added or removed, also.
The thing is a belt is modeled in terms of deltas rather than positions--there is no need to move each object each cycle. An object has a distance from the object in front. When the belt moves forward this relationship does not change--no need to update every pointer (and there can be a *lot* of belts in the game!) If the head of a belt can't move you only need to update one delta--the gap between the first free item and the stuck item in front of it and that value can already be known, no need to search. If you move the free item up against the stuck item you walk down the belt to find the new first free item.
You only need to modify the belt model if something is either added or removed from the belt. Objects get removed only by inserters, inserters examine only one cell of the belt, grabbing anything in that cell that matches what they are willing to grab (if they are feeding a machine they will only grab what the machine wants, otherwise they'll respect the filter list assigned to them.) When something gets added to a belt you add it to the list and update the delta of the object behind. No general update of the belt is needed in any situation, any more than you need to do anything to the items in a queue as you add and remove items.
Factorio is a game about optimization and the developers did a very good job of applying that idea to the game math. That is, until the masses of asteroids in the Space Age DLC.