Industry superannuation fund UniSuper has boosted its holding in Transurban by $200 million, acquiring a stake at a 6 per cent discount to the current price.

"Our entry price for the latest investment (of $200 million) was about $5.53, which compares favourably to the current price of around $5.90," UniSuper chief investment officer John Pearce wrote in an update to members.

The higher education and research sector super fund bought the stake in March when global investment management firm CP2 sold down a $632 million interest in Transurban, after its clients concluded they had too much exposure to toll roads in their portfolios.

"In such situations, big investors which are able to make quick decisions (literally overnight) are best placed to pick up the shares at a discount to the market price, which is exactly what we did," Pearce said.

"We expect the investment to create excellent value for our members and remain on the lookout for similar opportunities."

Transurban is an ASX top 50 company that owns and operates a portfolio of eight toll roads.

The company was expected to deliver a dividend yield of 5.5 per cent over the 2012 financial year based on UniSuper's entry price, Pearce said.

"When you consider that government bond yields are currently around 3.5 per cent, the attractiveness of the Transurban yield is self-evident," he said.

He said he also expected the dividend yield to steadily increase in line with the growth in tolls and traffic volume.