Traffic on the East West Link in the morning peak is expected to have slowed to 20-30 km/h by 2031 as worsening congestion pushes the road close to capacity just 12 years after it is due to open.

The East West Link is forecast to carry 80,000 vehicles a day on opening in 2019, increasing to between 100,000 and 120,000 a day by 2031, modelling shows.

Speaking at day four of the planning panel hearing on the major project, traffic expert Stephen Pelosi said the toll road would reach morning peak capacity by 2031. The most effective way to ease congestion would be to apply a higher peak-hour toll to reduce the number of discretionary trips.

''If it's reaching 120,000 we're at a position where we're reaching capacity,'' Mr Pelosi said. ''Unless you intervene in some manner and manage the toll rate to influence demand, you get a situation where you're near capacity.''

Mr Pelosi, a transport planner and traffic engineer who has worked on several major road projects in Victoria, was giving an expert witness report on behalf of the Linking Melbourne Authority, the state authority in charge of delivering the $8 billion link.