Prime Minister David Cameron has promised that HS2 will not take up an "unfair share" of the government travel budget.
Speaking on the Andrew Marr show, he said the government would not spend "unlimited money" on the project and said they would be sticking to the £42.6billion limit.
He also explained his reasons for pursuing the plan.
This is the Government that delivered the Olympics on time and on budget. We are delivering Crossrail - the biggest construction project anywhere in Europe - on time and on budget. HS2 is going to happen.
The west coast main line is full. We have to build another one. The choice is do we build an old-style Victorian one or do we build one of the new high-speed lines?
I think people all over the country are worried that HS2 is going to take up too much money.
In the next Parliament, we will be spending more than three times as much on other transport projects as we will on HS2.
It's not taking up an unfair share of the budget.