Fears the economy would hurtle over a "construction cliff" with the end of the mining investment boom are being soothed by the states.

This year’s round of state budgets contained notable capital expenditure plans with transport projects shaping up as a key driver of future investment activity.

NSW in particular has announced infrastructure spending of more than $61 billion over the next four years, bolstered by its policy of “capital recycling”.

Deloitte Access Economics says using the proceeds from privatisation for new infrastructure projects is a useful funding mechanism in a constrained fiscal environment.

But in its quarterly investment monitor it warns that it is important that appropriate cost-benefit analysis is undertaken for all these major investment projects.

“That analysis is arguably even more important when projects are funding by the public sector,” Deloitte partner Stephen Smith says.

The June quarter investment monitor says the value of outstanding projects across the nation fell by 0.4 per cent compared with three months earlier to $875.4 billion, but only by just 0.2 per cent over the year.

This includes 81 new projects announced in state budgets, contributing $21 billion to the total value.

Mr Smith said the value of projects have barely budged over the past year due to the relatively static value of resources projects under construction, which have made up more than 50 per cent of all investments since 2011.

However, on current trends he expects this to slip back below 50 per cent within the next year.

The value of definite projects (those under construction or committed) totalled $428.9 billion as of the June quarter, while planned projects (those under consideration or possible) totalled $446.5 billion.

By Colin Brinsden