Martin,

You haven't completely blown a fuse, but I think horse-drawn wagon won't be the answer. The input/output problems are too much of an issue in modern cities. Your idea of a high-tech wagon is intreuging and I think construction would pretty straigh-forward.

Looking at human-powered vehicles seem to me to be a much better solution. While in China I watch in amazement as people bicycled past carrying things like five medium pigs or a large fridge.

Amazing Cargo Bikes

The Buscycle

The downside is a lot of cities have rules against such devices, especially home-built ones. They fear someone might get hurt by them. I suspect the same thing would apply to wagons.

-Blast