Some 30 billion kronor would be spent on a line linking Järna in the Stockholm region to the rail network of Linköping, about 150 kilometres to the south-west.
The government said the plans would lead to "more frequent, faster and more punctual" rail services that would not only benefit passengers and rail cargo users, but also create jobs and growth.
Another 20 billion kronor would go towards a temporary increase in the operational budget and maintenance of the national railway until 2025.
The centre-right government also plans to set aside 5 billion kronor for the
Gothenburg-Borås line, which is the last stretch of the Stockholm-Gothenburg link.
Swedish travellers were hit by a series of train delays in August, prompting the news agency TT to describe a "black month" for the rail network.
The government added that other plans are in the pipeline to improve the rail links which would be announced when it presents its 2013 budget on September 20.
It said a law on infrastructure would also be announced in the autumn.