Investors burnt by the collapse of the company that operated Brisbane's Clem7 toll tunnel will receive a $121 million in a court settlement.

Lawyers Maurice Blackburn say they have reached a conditional settlement with engineering consultancy group AECOM over what the class action lawsuit claimed were misleading traffic forecasts for the tunnel.

The class action involved investors in RiverCity Motorway, the Clem7’s then owner, which collapsed in 2011 with $1.3 billion in debts.