The impact of improved highways on Indian firms

India's Golden Quadrilateral Program, a major highway project, aimed at improving the quality and width of existing highways connecting the four largest cities in India. It affected the quality of highways available to firms in cities that lay along the routes of the four upgraded highways, while leaving the quality of highways available to firms in other cities unaffected. This feature of the project allows for a difference-in-difference estimation strategy, where status on and off the improved highways, and distance from them, are used as treatment variables. This strategy is implemented using data from the 2002 and 2005 rounds of the World Bank Enterprise Surveys for India. Firms in cities affected by the Golden Quadrilateral highway project reduced their average stock of input inventories by between 6 and 12 days' worth of production. Firms in cities where road quality did not improve showed no significant changes. The reduction in stocks of input inventories also varied inversely with the distance between the city in which a firm was located and the nearest city on an improved highway. Firms on the Golden Quadrilateral were also more likely to have switched the supplier who provided them with their primary input, suggesting that they saw reason to re-optimize their choice of supplier after the arrival of better highways. Consistent with these findings, firms on the improved highways reported decreased transportation obstacles to production, while firms in control cities reported no such change.