There is no 1 root cause. There is a lack of empty containers in Asia and a glut in the US. There are all sorts of constraints in the US like how high a stack

There is no 1 root cause. There is a lack of empty containers in Asia and a glut in the US. There are all sorts of constraints in the US like how high a stack is allowed to be (presumably for safety or sightly reasons). There are too many containers in the US on chassis so there is a shortage of empty chassis available to take to ports. Distribution centers are reporting that truck drivers are dropping off trucks overnight and blocking their loading docks. There are reports that loaded cargo trains are unable to load so they are just blocking critical tracks. The Twitter thread is from the CEO of FlexPort which is a startup trying to make ports and trust transport more efficient. He is pointing out critical paths in the port nodes of the supply chain graph, but the root causes are many and not necessarily all within his visibility.