The slowdown will affect these lines, which include parts of the busy high-speed lines between major cities Stockholm, Gothenburg and Malmö, according to a Transport Agency (Trafikverket) report.
“When we notice that they are worn we have to reduce speed for it to be safe,” press officer Bengt Olsson told public broadcaster SVT on Monday.
Speed and weight limits will also be cut on 16 railroad bridges in Sweden.
In some part of southern and western Sweden, the tracks are in such a poor state that speeds will be reduced to 130 kilometres an hour, down from 200 km/h.
“It's just like you can't drive a couple of hundred kilometres an hour on a gravel road. You have to adapt your speed,” said Olsson.
The state of Sweden's railways has been a hot topic in the past year, with the centre-left government allocating 200 million kronor to urgent upgrades in their upcoming autumn budget proposal.
Next year's slowdown is likely to put another dent in Swedish trains' time-keeping record. According to figures revealed last month, Sweden's high-speed trains are the worst in Europe when it comes to arriving on time, a problem blamed mainly on maintenance.
Many of Sweden's rail tracks are old, with some in use for as long as 150 years.
Separate figures released earlier this year showed that one in three of the country's trains were delayed in 2015.