The Sydney-based company, which already operates Melbourne's CityLink toll road and will operate the under-construction West Gate Tunnel, is seeking to acquire Horizon Roads, which has a concession over the EastLink freeway until 2043.
The Australian Competition and Consumer Commission is concerned the proposed acquisition could deter the emergence of a key rival to Transurban for future toll concessions.
"Without the transaction, Horizon Roads could provide an alternative toll road owner or operator with the opportunity to gain some of the capabilities and incumbency advantages held by Transurban," ACCC chair Gina Cass-Gottlieb said in a statement on Thursday.
"This includes Horizon Roads' traffic modelling capabilities, which may be leveraged to bid competitively for future toll road projects in Victoria."
Given Transurban already owns a significant portion of Melbourne's toll road concessions, there are concerns gaining ownership of EastLink will further advantage it when competing for future projects.
The ability of the Victorian government to constrain Transurban and promote competition for future toll road contracts will come under the microscope of the ACCC's review.
The regulator is also examining the impact of the takeover on the supply of electronic tolling services to motorists, the supply of tolling systems to toll road operators, and competition between EastLink and CityLink.
As well as its Melbourne assets, Transurban operates eight Sydney toll roads, eight Queensland assets and three in North America.
A spokesperson for Transurban said the company would continue to proactively engage with the ACCC.
"We are of the view that there would be no substantial lessening of competition from the potential acquisition,'' the spokesperson said.
The ACCC will accept public submissions to its review into the acquisition until July 14.
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