The total value of infrastructure projects under way or in the pipeline in the ACT increased to $4.8 billion at the end of 2018, according to figures released on Monday by Deloitte Access Economics.

That marked a 13 per cent, or $552 million, increase from the September quarter, and an 16 per cent bump on the December 2017 level.

Almost $2.8 billion worth of projects are under construction in the ACT, with a further $1.8 billion worth of infrastructure investment being considered.

The planned $500 million redevelopment of the Australian War Memorial is set to boost the territory's infrastructure spending figures, which will take a hit from completion of stage one of the light rail. Commercial construction spending has grown by almost a third in the past year, while the territory's retail, health and education sector continue to perform strongly, according to the report.

Nationwide, infrastructure spending dropped to its lowest level in a decade, as a surge in public projects failed to compensate for a drop-off in interest from the private sector in sinking cash into new upgrades.

The total value of nationwide infrastructure spending fell to $679.1 billion at the end of the December, a 3.8 per cent drop on the September quarter result.

Over the past year, the total nationwide value of committed projects has dropped by more than 52 per cent, while the value of those under construction slipped by 20 per cent to $244.4 billion.

Deloitte Access partner Stephen Smith said the state of the economy, solid business profits, low borrowing costs and the lift in public infrastructure spending all pointed to good times for private-sector spending.

But it was clear the private sector, led by the nation's miners, was holding back rather than sinking more money into productivity-enhancing projects.

"A number of leading indicators, including the capex survey conducted by the Australian Bureau of Statistics and the value of building approvals, remain relatively subdued," he said.

"There are also doubts about whether the mining sector will be a driver of business investment in the short term.

"Despite the fact that profits have grown by almost 350 per cent in the past two years, investment in new capacity has been weak."

While the overall value of projects being considered or being built fell during the quarter, there were some sizeable cost blowouts which softened the drop. These included a $700 million increase in the cost of Rio Tinto's Koodaideri iron ore mine and a $5 billion lift in a major floating LNG project.

NSW continues to lead the way of the states and territories with investment up 9.7 per cent to $153.5 billion over the past year.

But Deloitte cautioned that this year would likely be the peak for NSW, with one-off factors including the drying up of proceeds from privatisation to fund new infrastructure likely to weigh down spending in 2020 and beyond. This includes the completion of major projects under way, including the $3 billion NorthConnex and $2.1 billion Sydney CBD light rail projects.

Victoria has enjoyed the biggest lift in spending over the past year, up by 29.2 per cent to $103.5 billion.