There isn't a direct bus from Pioneer Hall to Downtown Disney. You'll have to use the FW transportation system to get to that bus. Near Pioneer Hall where the Trail's End Restaurant is, there is a bus stop. From there, take any bus labelled "Outpost" to the bus stop at the Outpost Depot. From the Outpost you can catch the bus to Downtown Disney. Chip 'n Dale Express had a wonderful map of the transportation system through FW a few months back that helped me tremendously when I went there for the campfire one night. I'd try to link to it, but I'm not sure how to do that. Hope this helps though!