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Percentage answer

Thank you for publishing the articles on the Boston Central Artery project in the July issue. I would like to clarify the cost of the instrumentation programme ('Watching Brief').

The total anticipated cost of the project was correctly stated as US$10.8bn, while the $10M cost of the instrumen- tation programme referred to is only the cost of reading the instruments and reporting the data to the management consultant (Bechtel/Parsons Brinckerhoff) in a specified format. This represents about 0.09% of project cost.

Total cost of the instrumentation programme, including supplying the instruments, installation, collecting the data and data management (but excluding the cost of designing the programme) is nearly $40M, hence nearly 0.4% of the project cost. When expressed as percent of construction cost, the number is of course significantly higher. Also, the percentage varies with the complexity of each particular construction contract and for the complex downtown sections alongside major buildings, the total instrumentation cost is substantially greater than 1% of construction cost.

Having written these numbers, I must add a caveat, because people sometimes ask me what percentage of construction cost should be spent on instrumentation. I remind the questioner of the golden rule: 'Every instrument on a project should be selected and placed to assist with answering a specific question: if there is no question, there should be no instrumentation'. In Boston there are very many questions.

John Dunnicliff, Devon

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