• External market conditions, including steel price increases, industrial consolidation and other industry dynamics that limited the number of potential competitors.
     
  • Design complexity, in that the proposal was for a relatively long, asymmetric self-anchored suspension span. Nothing like this has ever been built before, and the initial optimism on cost was highly unrealistic, says the report. Estimates for the entire project have been driven steadily upward by a growing realisation of the cost and complexity of this section of the work.
     
  • Time - the schedule was extended repeatedly, which caused estimates to escalate because of inflation and increases in overheads.

    A decision on the bridge design project is due to be taken in a few months. A simpler viaduct structure is now the preferred alternative.