What is the most common cause of big projects over running on their estimated budget? For example, I recently learned that the HS2 train line in the UK will be nearly £75bn over the estimated budget! How was the estimate so wrong?

Question

What is the most common cause of big projects over running on their estimated budget? For example, I recently learned that the HS2 train line in the UK will be nearly £75bn over the estimated budget! How was the estimate so wrong?

In: Engineering

Answer 1

Because when there’s no consequences for going over an estimate, there’s no real incentive to make sure you stick to your estimate or to estimate a number you can stick to.