No one likes white elephants. But some mega-projects are simply unbeatable. One example is India’s Golden Quadrilateral highway project, constructed between 2001-2012. In a new paper, Ghani, Goswami and Kerr write:

Source: Wikipedia

We exploit a large-scale highway construction and improvement project in India, the Golden Quadrilateral (GQ) project. The analysis compares districts located 0-10 km from the GQ network to districts 10-50 km away, and we utilize time series variation in the sequence in which districts were upgraded and differences in the characteristics of industries and regions that were affected. Our study employs establishment-level data that provide new insights into the sources of growth and their efficiency improvements.

The GQ upgrades stimulated significant growth in organized manufacturing (formal sector) in the districts along the highway network, even after excluding the four major cities that form the nodal points of the quadrangle. Long-differenced estimations suggest output levels in these districts grew by 49% over the decade after the construction began. This growth is not present in districts 10-50 km from the GQ network nor in districts adjacent to another major Indian highway system that was scheduled for a contemporaneous upgrade but subsequently delayed. We further confirm this growth effect in a variety of robustness checks, including dynamic analyses and straight-line instrumental variables (IV) based upon minimal distances between nodal cities. As the 0-10 km districts contained a third of India’s initial manufacturing base, this output growth represented a substantial increase in activity that would have easily covered the costs of the upgrades.

Decomposing these aggregate effects, districts along the highway system experienced a significant boost in the rate of new output formation by young firms, roughly doubling pre-period levels. These entrants were drawn from industries intensive in land and buildings, suggesting the GQ upgrades facilitated sharper industrial sorting between the major nodal cities and the districts along the highway. Despite a substantial increase in entrant counts, the induced entrants maintained comparable size and productivity to control groups. The young cohorts, moreover, demonstrated a post-entry scaling in size that is rare for India and accounted for an important part of the output growth.

Of course these findings should not come as a surprise to anyone who has seen the rapid growth along the $360m Thika Superhighway in Nairobi and Kiambu counties in Kenya — the African Development Bank (a key financier) estimated the project to have an internal economic rate of return of 30%. Which is precisely why Harambee House ought to consider fast-tracking the construction of a dual carriageway linking Mombasa to Busia and Malaba.