Toll tariffs will increase in line with the consumer price index (CPI) on May 24, the SA National Roads Agency Limited (Sanral) said on Friday.

"Any adjustments to the tariffs are based on the preceding twelve months' CPI. The average CPI adjustment for Sanral toll tariffs is 5.8 percent," it said in a statement.

Transport Minister Dipuo Peters approved the tariff adjustments proposed by Sanral early in May and the adjustments were gazetted on Friday.

The only toll plaza that would not be affected by the increase was Swartruggens.

"We use the inflation rate as a guide, as we at the national roads agency do not want to increase road usage costs beyond what is reasonable," spokesman Vusi Mona said.

Electronic tolling in Gauteng would also not be affected.

"E-toll tariffs in Gauteng became effective in the beginning of December 2013 and therefore the first annual adjustment may only be in March 2015," said Mona.