We measure the impact of low cost transport by rail in Malawi on the dispersion of agricultural commodities prices across markets, by exploiting the quasi experimental design of the nearly total collapse of domestic transport by rail in January 2003, due to the destruction of a railway bridge at Rivirivi, Balaka. Estimations are based on monthly market prices of four agricultural commodities (maize, groundnuts, rice and beans), in 27 local markets, for the period 1998-2006. Market-pairs connected by rail when the railway line was operational, are intervention observations. Railway transport services explain a 14% to 17% reduction in price dispersion across markets. Geographical reach of trade varies by crop, most likely related to storability and geographical spread of production. Perishability appears to increase impact reflecting the lack of intertemporal arbitrage. Overall, impacts are remarkably similar in size across commodities.