Port of Tauranga chief executive Mark Cairns believes Labour's proposed commuter rail plan can't work with current infrastructure.

Labour unveiled the plan in Tauranga on Monday, in which commuter rail options between Auckland, Hamilton, and Tauranga would be made available under their government.

Mark says he doesn't want to be seen as negative, but although he admires Labour's vision, he can't see it working.

'We run 74 trains a week, moving to 90 over the next 12 months. We've experienced 64 per cent growth in the last two years.

'Where I think it is flawed is that it can't work on the same line. The railway line between Hamilton and Tauranga is single-track. I believe they're considering running the commuter trains at 160km/h, even though the line is rated for 80km/h.

'You can't just have a train doing 160km'h passing a freight train doing 75km/h on the same track – they just can't pull out and pass them.”

He says with 90 trains a week, the single track would already be under pressure when Labour intends to introduce its policy.

'Given 41 per cent of New Zealand's exports come through the Port of Tauranga at the moment, you would think that would be an important consideration in developing the policy.”

He says the issue isn't about sharing the line, but that another line with a wider gauge would be required altogether.

'There's been a suggestion by Labour that Port of Tauranga has exclusive use of the line. We're one of the largest users of the line, but we don't have exclusive use.”

Greater Tauranga spokesperson Heidi Hughes disagrees, saying passenger rail does not mean sacrificing freight.

'It is just as important to a congestion-free network to have trucks off the roads as it is to have the choice to be able to travel by train.

"Regarding capacity on the line, the Ministry of Transport reports the capacity of the East Coast Main Trunk Line to Tauranga is four trains per hour, or just under one hundred trains per day.

'There are currently up to 30 trains a day on this line. Stage 1 of the proposal adds a grand total of two passenger trains per day: one to Tauranga in late morning, one from Tauranga in the early afternoon.”

She says the assertion that double-tracking is required to add two trains a day is simply ‘incorrect'.

'In the subsequent stages of the proposal, a substantial portion of the budget is indeed allocated to lengthening passing loops and creating long stretches of double track between Hamilton and Tauranga.

'This will increase the capacity of the line and allow a regular hourly service each way all day, as well as increasing the performance and capacity for freight sharing the line.

'In 2012 a series of passing loop extensions built by KiwiRail, doubled the capacity of the East Coast Main Trunk Line for a mere $13 million, with a very high return on investment.

'Operating a trunk line with both freight and passenger trains on the schedule isn't rocket science, in fact it's the norm in most developed nations.”