Winston Peters and Simon Bridges challenged each other's athletic ability in Parliament this afternoon in a debate over light rail.

The project, an early campaign promise from Labour, would take light rail from Auckland's CBD to the Airport. 

It was revealed this week that a second project from the Superfund and Canada's CDPQ Infra group for the bid, and is currently being considered alongside the NZTA proposal.

The project was set to be open in 2021, but it has faced criticism over delays as Cabinet is yet to pick one of the proposals.

Asked if that date was still the outcome, Peters, standing in for the Prime Minister, says the project's unlikely to be finished by that point. 

Bridges then offered a challenge.

"If the project is complete by then, would the right honourable member join me in a running race down Dominion Road, or am I fairly safe in that prediction?

Over the protests of Speaker Trevor Mallard, Peters responded: "If there was a race between him and me, I'd give him a 30 metre start."

Earlier this year, the National leader said he'd run down Auckland's Dominion Road in his underpants if the light rail project for the city's completed by 2021.

In Parliament today, Peters said they would endeavour to save the New Zealand public from that outcome.