Australia's toll road king, Transurban, has defended above-inflation increases in charges for some of its motorways as the result of deals struck many years ago by state governments after Sydney motorists helped deliver it bumper profits.

In further evidence of the stellar returns Transurban is making in NSW, toll revenue from its Sydney toll roads – which include the M2, the M5 and the M7 – surged almost 14 per cent to $799 million for the year to June.

CBRE Clarion's new infrastructure fund has allocated 4 per cent of its $500 million in AUM to Transurban. Credit:Danielle Smith

At present, tolls on the M2 and the Eastern Distributor are increasing at 4 per cent a year, significantly outpacing the annual rate of inflation of about 1 per cent.

In highlighting that it operates in a "heavily regulated environment", Transurban chief executive Scott Charlton sought to explain the toll increases by pointing out that they were the result of concession agreements set by the state governments.