Source: adapted from Flyvbjerg, B. (2009) "Survival of the unfittest: why the worst infrastructure gets built—and what we can do about it", Oxford Review of Economic Policy, Vol. 25, No. 3, pp. 344-367.
Inaccuracy of Transportation Project Cost Estimates by Type of Project
A database of 258 transportation infrastructure projects spanning the world reveals systematic and very high cost overruns; 9 out of 10 projects. They are on average 44.7% for rail, 33.8% for bridges and tunnels and 20.4% for roads. Standard deviations are also very significant, particularly for bridges and tunnels, which underlines the high risk of transport infrastructure projects. Additionally, there appear to be no significant geographical and temporal differences in cost overruns.