I hate to be picky but ...
Cars are built from iron, Steel, and Chemicals. Cars are driven on Concrete Highways.
The infrastructure ought to be considered devastating.
Australia will cease local production of cars by the end of 2017. Fossil fuels will be used to ship cars into Australia from overseas. Overseas the iron, steel, cement and chemical plants will continue to spew toxins and burn energy.
Australia will continue to pave its highways.
We know that people get Washed Overboard and that Fishing Vessels sink.
We figure that the Drowned Bodies are eaten by fish and other marine creatures.
We know that the foot is connected to the shin bones by Ligaments and Cartilage and other soft stuff, and is relatively easily disconnected from the leg bones..
We know that flesh decomposes and the bacteria give off gases (which is why drowned canoeists surface after three or four days).
We know that Sneakers are pretty well air-tight if the sole is uppermost.
So why are we surprised that feet-in-sneakers wash up on shore?
I would be surprised if they didnít occasionally wash up on shore.
I would expect the numbers to rise over a period as (a) more humans on the planet go fishing in little wooden boats and (b) more people on the planet take recreational walks along the shores.