Measurement of iron trade, specifically in used cars

 Is trade in iron - specifically in the case of used cars -difficult to measure?

A: Below, please find comments on your statement "...that it is hard to measure statistics on iron exports.  Apparently, because there is a $2500 barrier above which exported products must pass to be counted. And obsolete iron-containing materials (e.g., old cars), though of great mass, often slip under this barrier. So the opportunities lost to recycling, had the cars stayed in the country, are hard to gauge."

The $2500 threshold is used in the United States. Your assumption here is that individuals would do exports of used cars with a value below US$ 2500 on a large scale. A truckload or shipload of used cars would certainly surpass the $2500.

Also, given registration and insurance issues, there are, in fact, special regulations for selling used cars abroad. You would need to check this with the Customs authorities. To complicate matters, the US Census Bureau exchanges imports and exports data with Canada; to be precise, the USA's exports with Canada are taken from the reported Canadian imports with the USA (and vice versa). We do not exactly know what the Canadian import threshold is.

To be more exact, one would need to check the exact regulations of transporting a used vehicle from the USA to any other country.