No, you have to look at the margin. The other 99 people are already there, and you have to choose whether or not to drive; you slow down everyone after you, but you don't slow yourself down.
Everyone before you chose to inconvenience all comers before and after. In a situation like this, especially because it's iterated every day, these people are clearly choosing to slow, and be slowed by, everyone coming after them. Being on the road first doesn't give you moral superiority.
In some situations the margin of newcomers is a fair way to look at it. But with drivers on the road, these people are all getting up in the morning and choosing to use this road at the same time. It is a continuous reaffirmation, day by day, that this is the path they want, no matter who they slow down, and they accept being slowed in return.
Each driver is causing themselves 10 and everybody else 990. Your analysis acts as if people make decisions as a group.
"Each driver is paying their exact cost." Yes, but on the margin each driver can only choose a small chunk of their cost. Seriously, have you looked at the enormous literature on this? One major annoyance on HN is the way CS people assume that they can independently grok the intricacies of any field.
I'm not trying to argue about the intricacies, I'm pointing out that your original example was terribly flawed.
Assuming drivers actually consider their effect on congestion, they are willingly accepting the congestion of those coming after just as much as they accept the congestion they cause. (Most probably don't consider it but that's beside the point) Most importantly, the drivers are choosing to use the road every day even after seeing the final congestion every day. That's not a marginal decision. They are choosing to accept the final congestion.
But even if you insist on a marginal explanation with actors incapable of anticipating future cars, the average driver is intentionally accepting and causing 500 with past cars, and unwittingly accepting and causing 500 with future cars. Versus your characterization of them only intentionally having 10 delay.
Framing it as a new car 'paying a pittance more' is nonsense. The twentieth car either doesn't travel or attempts to pay 200 to travel. Comparing 190 to 200 is meaningless, because they never had the chance to travel at 190.
You need to count the people who would like to use the road, but must choose their next-best option because the road is too congested for them to use (either that time, or in general).
There is a congestion externality on them despite not using the road.
That's fair, but it probably leaves drivers feeling at least half of the effect they cause, rather than the fraction of a percent implied by seizethecheese.
