Slowboats

During the occupation of Earth, more and more attacks were made against Hegemonic forces. Early in the occupation, in an attempt to prevent (or cut back on) Insurgent attacks, the Hegemony mandated that no aerial vehicle would be allowed to travel outside of a starport at greater than ~52 mph (translated from the Hegemonic unit of measurement). Any that exceeded that limit would be destroyed without warning (whether it be by orbital destruction, torpedo emplacements, or invisible nano-swarms).   Over time, an entire terrestrial industry grew up within the confines of the 'slowboat edict'. The sky barges were cobbled together (or fabbed whole cloth) with the edict in mind. Most are hardwired not to allow speeds greater than 40 or 45 mph.   Most population centers have 'docks', or collections of piers or spires, that allow for the easy transportation from the slowboat (a few hundred feet up on average) to the ground below.