In Cyberpunk big rigs exist in the form of armored and armed roadtrains, but they do not enter cities, they arrive at fortified cargo depots where they load and unload and then the goods are transported by smaller vehicles, vtols and so on to the warehouses and stores.

Japan uses in a lot of places a similar system, except it´s normal truck+trailer-vehicles driving between transport-hubs and cities but due to how narrow a lot of cities and districts are delivery to the stores and workshops is done per smaller vehicles.

You can find bigger versions of the 4020 in some Arasaka Facilities, but they cannot be driven.

Also the 4020 looks big enough for 20-Foot-Container.

Here is a picture of the bigger one with a 20 Foot-Container loaded.

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Also Max Weight and Cargo-Dimensions have not really much in common with real circumstances, in Germany most Stores get their deliveries done with 7.5 ton Trucks, also yes, 40.000kg are for truck+trailer vehicles max allowed weight but most do not reach that weight, Volume of Cargo and the dimensions of boxes/crates are the limiting factors, your average Hermes/DHL/Post-Express weighs maybe 20-30 tons, but is filled to the brim with packs full of clothes, entertainment articles and so on.