All construction cost figures that I sign my name to adjust currencies for purchasing power parity, or PPP. In other words, I convert currencies across countries in PPP terms, not exchange rate terms. This is not how everyone else does this; the World Bank analysis of global high-speed rail costs converts currencies by exchange rate, and, since the yuan is undervalued, concludes Chinese construction costs are below world average, whereas in fact they are above average.
Because nearly all of the costs of the construction of infrastructure are local. Labor is almost entirely local, and materials are as well, since concrete is made locally rather than imported. Foreign expertise and machinery are internationally traded; in those cases, currency devaluations can lead to cost overruns, but the proportion of the cost that is traded remains low.
India: an indigenization plan from the 2000s was quoted as reducing costs by 10-15%. The rupee’s exchange rate value is lower than its PPP value by a factor of about 3.3; indigenization reducing costs by 10-15% is compatible with around 20% of the total value of the original contract being imported.
Philippines: I spoke with a DOTR planner, who said that 90% of the value of civil works is local, and only 10% is imported, such as foreign expertise and imported material; the planner said that rolling stock is imported, but our construction cost estimates exclude rolling stock when possible.
Why not wages?
Because while the bulk of costs are domestic, they are not labor in developing countries. In Turkey, which is not much poorer than Southern Europe, costs split as 20% labor (US: 55%), 40% permanent materials, 10% construction materials, 30% construction equipment. The 80% non-labor costs are mostly domestically-produced, at local wages, but also at local productivity. If Turkey could produce everything at the same productivity as a richer country, it would just be a richer country. This goes even more so for actually poor countries like India and the Philippines.
The impact of PPP
With PPP adjustment, GDP per capita ceases to be a significant correlate of construction cost per km, except through the tendency of poor countries to build more elevated and fewer subway lines. This was not the original intention of the adjustment, which was to smooth dollar-euro difference, but it’s suggestive that it’s correct and meaningful.