4 and 8 both get used in Japanese to convey totality: on all sides (四面楚歌) or in all directions (八方美人). Using them together increases this effect.
1. Accessible from everywhere/providing access to everywhere.
2. At the center of a comprehensive traffic network.
Like how the definition includes another yo-ji that makes use of the same 4/8 effect?
Note: Don't confuse the 4/8 in 四苦八苦 to mean "suffering from all sides." In this case, it actually refers to a specific number of pains and sufferings. See our post on it for more information.
From up here, looking at the way Osaka sprawls out below us, the roads run in all directions and the people coming and going are as small as ants.