Crash: thread 'main' panicked at 'Queue has spillover on Traversable::Lane ... sim/src/mechanics/queue.rs:91:17 about abstreet HOT 3 CLOSED

Thanks for the logs! The full weekday scenario on huge_seattle has loads of bugs -- this one is a known issue. (Getting a full day to complete without hitting permanent gridlock is only possible right now on the montlake map, which has lots of manual fixes to short roads / coupled intersections.)

I'm pretty sure this particular problem happens when there's a nice cycle of laggy heads (see https://github.com/dabreegster/abstreet/blob/master/docs/articles/trafficsim/article.md#exact-positions). I need to make an easy test case to repro this (using map_editor to create a synthetic map) and then think through what should happen here.

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I happened to get an easy repro of this problem. When a car is half in a turn, half on the end of the last lane, they're a "laggy head. That influences the front position of the first car on a lane; the laggy head prevents the first in the queue from being at the very end of the lane. get_car_positions recurses to figure out exactly where the back of the laggy head is. I have to figure out how to break the recursion and decide where the back of a car is for this case

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I think this particular issue is gone. https://github.com/dabreegster/abstreet/projects/2 the best way to track current work on getting simulations on large maps to work properly.

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