- 1850-1890 was a period of high protectionism, highest tariffs on imports in the US history.
- A good approximation of share of traded goods in the railroads would be the share of imports+exports in the GDP. Together, exports and imports were not more than 15% of GDP. Source: https://www.nber.org/system/files/working_papers/w4710/w4710..., Table 3.
- railroads transported a lot of agricultural products and also passengers, and were hugely profitable from that. I doubt they would recover any cost by transporting porcelain and whatever other goods China exported at the time.
- "But that answer is wrong, as can be shown by examining historical records of the time." - citation needed.