Train passengers on the Wellington region's Hutt Valley and Kapiti lines will have 1000 more seats to choose from in morning and afternoon peak times starting tomorrow.

The last of 83 sets of two-car Matangi units were added to the lines in September, ending a nine-year, $430 million upgrade to the train fleet.

The upgrades began in 2007 with refurbished carriages on the Wairarapa service, Greater Wellington Regional Council public transport team leader Paul Swain said.

"Our passengers had been travelling on trains and carriages that were up to 60 years old and were becoming increasingly unreliable," he said.

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The 24 refurbished carriages on the Wairarapa service cost $25 million, while the Matangi units were delivered under budget at $406 million.

Contracts for improved bus services are out for tender and will come into effect mid-2018.