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In the context of Figure 4, the P50 cost is represented as âcâ dollars. The P50 estimate is one with equal chance of project overruns or underruns up till when the project scope can be finalised. The P90 value is an estimate of the project cost based on a 90% probability that the cost will not be exceeded.his arises as the P90 cost estimation was adopted at the early stage during project scoping. Had the P50 cost estimate been adopted, there would have been a deviation of $7 million between the actual ($69 million) and budgeted P50 figure ($62 million). The project would have been under-budgeted.
DOCS_AND_FILES-#5559369-v26-EST_600_-_Estimating_Manual_for_Road_and_Rail_Projects.DOC Page 24 of 81 1.8 Duplicate Estimates Where the project estimate is anticipated to have a P90 Project Estimate value exceeding $25 million a duplicate estimate should be sought prior to seeking funds for the project.OCS_AND_FILES-#5559369-v26-EST_600_-_Estimating_Manual_for_Road_and_Rail_Projects.DOC Page 38 of 81 elements only and the estimate prepared on this basis. Examples are road cost per km and bridge costs per square metre of deck area.