*$4b in new capital spending on infrastructure

*$32.5b total investment in infrastructure over next 4 years

*Transport takes biggest slice of infrastructure money

Infrastructure is one of the key themes of the Budget, with $4 billion in new commitments for new rail projects, schools, defence upgrades, and prison beds.

That is part of a $32.5 billion total investment on infrastructure over the next four year - through Kiwirail, Housing NZ, the NZ Transport Agency and others.

Finance Minister Steven Joyce said it was the biggest investment of new capital in infrastructure "by any government in decades". A further $7 billion in new capital had been put aside for the next three Budgets.

The biggest share of the $4b in new capital funding is going towards transport, where the Government has committed $436m into Auckland's City Rail Link and $450m into state-owned rail company Kiwirail.

Another $812 million is going into repairing quake-damaged State Highway One around Kaikoura, and $98 million will be invested in Wellington's rail network.

The other key investments in infrastructure are:

• $39 m to begin construction of six new schools in the next four years, two school expansions and 300 new classrooms.
• $150m to build or upgrade hospitals around New Zealand.
• $576m for new defence equipment, including a new support vessel for the navy.
• $763m to expand prison capacity around New Zealand.
• $100m to free up more Crown land to build 1200 houses in Auckland.
• $63 for new water storage infrastructure in regional New Zealand.

A $1 billion fund to support housing developments was announced last year. However councils are yet to begin tapping into it because they have not completed their funding proposals.

Over the next four years, the NZ Transport Agency will spend $9.2 billion on 540km of new state highways.

As announced last week, Housing NZ will invest $2.2 billion in building thousands of houses in Auckland.