It has been determined that the building proposed for the tunnel control centre cannot be constructed on site 3A and after assessment of options the Roads and Traffic Authority (RTA) has decided to seek modification of the approved Cross City Tunnel project. The proposed modification is to relocate two of the three stories proposed for site 3A which would accommodate the tunnel control centre supervisory facilities onto the adjacent site 2A. A singe storey building would be constructed on site 3A to primarily accommodate maintenance facilities. This review of environmental factors considers the environmental impacts of the proposed modification. It presents details of the proposal assesses the existing natural and social environments, describes the potential impacts on the environment and presents safeguards to minimise and or avoid these identified impacts.