Network Rail is to claim train delays have fallen by up to a fifth since it took over direct control of day-to-day track maintenance last year.
Critics said Network Rail wouldn't be up to the job
The company has now re-employed 16,000 maintenance workers previously employed by private firms.
On Wednesday the company will say in the first three areas where maintenance has come back in-house delays have fallen by 21%.
Network Rail said it was proof their critics had been wrong.
A spokesman said critics had last year claimed Network Rail would not be up to the job.
BBC transport correspondent Tom Symonds said Network Rail would also soon have primary responsibility for train punctuality.
It would be under pressure from the government to bring in quick improvements that passengers would notice, he said.
Network Rail replaced Railtrack in 2002 and the following year announced that all maintenance work would be brought back in-house.
This had previously been subcontracted to private engineering companies, and standards had been criticised.