After the 1855 railroad, crossing the isthmus is cheap. And requires/
- coal from the US
- locomotives from the US
- boxcars from the US
- rails from the US
- a roadbed constructed by unskilled Panamanians to plans by US engineers.
Before 1855, crossing the isthmus is expensive, and requires:
- Panamanian ranchers to breed mules
- Panamanian muleteers
- Panamanian workers to pack goods into mule packs
- Panamanian boatbuilders
- Panamanian boatworkers
1855 sees a sharp rise in cross-isthmus traffic, but the fall in Panamanian resources per crossing was big enough to create a presumption that there was actually a fall in demand for Panamanian resources upon the construction of the railroad.
Looks plausible. Worth pursuing. And, of course, the only alternatives to Panama before 1869 were the Horn and the Oregon Trail.