A temporary six-lane road will be built alongside Anzac Parade to allow for a tunnel to be dug for the $2.1 billion light rail line between Sydney's CBD and the eastern suburbs.

The temporary diversion will run along the eastern side of Anzac Parade between Lang Road and the Albert "Tibby" Cotter Walkway. Construction of the road near the Sydney Cricket Ground will begin in April, raising the prospect of potential delays for eastern suburbs commuters.

The government had originally planned for two sides of the tunnel under Anzac Parade to be built separately.