Speculation is mounting the government could delay or scrap the second leg of the line to Manchester.
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Rishi Sunak has repeatedly refused to say whether the HS2 high-speed rail line will run to Manchester, in a series of BBC regional interviews.
Speculation has grown as ministers have not guaranteed the second leg of the line, from Birmingham to the North West, will be built.
The prime minister said the government was ensuring “we get value for money”.
Responding to questions, he instead talked about local bus links and improving roads by fixing potholes.
The issue of whether the line to Manchester will go ahead could overshadow the Conservative party conference, beginning in the city on Sunday.
Questions over whether it will go ahead have hung over ministers for two weeks, after photographs of documents identifying possible savings for parts of the line north of Birmingham appeared in the press.
Mr Sunak and Chancellor Jeremy Hunt met earlier this month to discuss the much-delayed project, whose costs have ballooned since the first estimates were produced over a decade ago.
Work has already started on the first part of the line, running from London to Birmingham.
It was originally then meant to run to Manchester and Leeds. However, the leg to Leeds was scrapped in 2021 over concerns about the cost.
Speculation has also mounted that the leg to Manchester could now be delayed, or scrapped altogether.
There have also been suggestions the government could also decide that the leg to London could stop at Old Oak Common, a new terminus in the west of London, instead of Euston station, in a bid to save money.
The first estimate for the project in 2010 was for about £33bn. The most recent official estimate, excluding the cancelled Leeds leg, adds up to about £71bn.
However this was in 2019 prices, so it does not account for the spike in costs for materials and wages, for example, since the Covid pandemic.
Asked on BBC Manchester whether the line would run to the city, Mr Sunak said he was “not speculating on future things”.
Pressed on whether it was under review, he replied: “[the] government is always making sure that we get value for money out of everything we do”.
Adding that most journeys across the North West were made by car, he said repairing potholes on the roads was “priority number one that people raise with me”.
He also went on to talk about the importance of boosting local bus services between northern towns and cities, adding it was “the most popular form of public transport”.
Asked how he would travel to Manchester for the Tory conference, he said he would “probably” drive because of train strikes taking place this weekend.
Dozens of businesses and business groups, as well as several regional mayors, have urged the government to renew its commitment to HS2.
The government has not said whether separate plans to boost rail connections between Leeds, Manchester and Liverpool will go ahead if the line to Manchester is scrapped.
The scheme, branded Northern Powerhouse Rail (NPR), includes a mix of new and upgraded lines and is meant to use a section of the HS2 line from Manchester Airport to Manchester Piccadilly, the city’s main station.
Andy Burnham, the Labour mayor of Greater Manchester, has said scrapping the Manchester leg of the line would “rip the heart” of NPR.