According to this Danish study, worldwide transportation “megaprojects” exceed their projected costs by an average of 28%.

• In 9 out of 10 transportation infrastructure projects, costs are underestimated.
• For rail projects, actual costs are on average 45% higher than estimated costs (sd=38).
• For fixed-link projects (tunnels and bridges), actual costs are on average 34% higher than estimated costs (sd=62).
• For road projects, actual costs are on average 20% higher than estimated costs (sd=30).
• For all project types, actual costs are on average 28% higher than estimated costs (sd=39).
• Cost underestimation exists across 20 nations and 5 continents; it appears to be a global phenomenon.
• Cost underestimation appears to be more pronounced in developing nations than in North America and Europe (data for rail projects only).
• Cost underestimation has not decreased over the past 70 years. No learning that would improve cost estimate accuracy seems to take place.
• Cost underestimation cannot be explained by error and seems to be best explained by strategic misrepresentation, i.e., lying.
• Transportation infrastructure projects do not appear to be more prone to cost underestimation than are other types of large projects.