Your core gameplay loop is broken. Carts only go as fast as the first one, it sets the pace for all the rest unless you have longer wait times between them. Liked being able to adjust their speeds as they were going around the track but again this is hampered by the speed being set by the first cart on the track as it goes around. Maybe if the work day were longer, you would have more time to pace out the carts, but, that could get boring as there is no management going on by that point.
I think I like the idea of having to get a quota of carts out per day, with you then having to manage their speeds manually as they go around the track. Lots of micro-managing of the carts to make sure they go fast when you need them to and slow when you need them to do that. How to effectively achieve this I'm not sure I have any ideas on, but, I do feel that perhaps the track is too long as is. Takes too long for those carts to do a complete loop.
Regardless there doesn't seem to be any negatives to having a huge line or not adequately meeting the needs of the customers. Wasn't even any negatives for carts hitting each other. In the end I was able to send most of them off on slow carts and still get 1338 satisfaction points with the customers happy.