I have Human caravan wagons trying to leave while Dwarven caravan wagons are trying to enter, through a 3-wide corridor attached to the edge of the map. They aren't just moving slowly, they aren't moving at all. It may be the two ramps leading down are too close together for the wagons travelling in two directions to pass over/under each other. I haven't found anything I can dig out, or bridges I can lower, that fixes this. Anyone want to have a try at at?
Here's my save: http://dffd.wimbli.com/file.php?id=6392
Happens to me all the time. If you give the humans a new 3-wide path to leave, they will change course and take it. The dwarven wagons will continue moving, however, and may cause a new jam past where you freed things up. Eventually they'll start deconstructing wagons to clear the jam - but it takes months.
I switched over to having two depots with a 6-wide entrance that would branch into two 3-wide depot approaches. A drawbridge would control which was open. Or you could just forbid the human one when the dwarves arrive.
Yes, and I didn't believe you because it had never happened to me before. Sorry.
The jam was very near the edge of the map and just before two consecutive ramps leading to the surface. The first Dwarven wagon was on the ramps and the first Human one was nose-to-nose with it. There were two corners in the tunnel before the ramps and so there was not much room to dig more tunnels but I did try. The Humans were apparently all committed to the original exit and only jostled for better position heading towards that exit when I widened the space in the hopes that they would turn and take a new exit. Eventually the first Dwarven wagon deconstructed and another entered the map to take its place. This continued until all of the Dwarven wagons were destroyed. Then the Human wagons left.
I've since dug a second exit to the edge, identical with the first, and made a wide space where they join on their way to the depot. I don't know if that will help. I don't like to have two depots because I have had problems before with parts of the caravan going to one and the rest going to the other, and neither ever unpacking fully. I've also had problems when I tried to make them all go to the one depot by cutting off access to the other depot, but they'd already chosen the second depot. They didn't seem to be able to change target. Maybe that doesn't happen anymore?