The return to CBDs will be "sluggish" in 2021, traffic congestion will rise as people continue to shun public transport and waste will keep soaring due to the botched recycling of packaging thrown out after online shopping sprees, a national study on infrastructure after the pandemic has forecast.

Infrastructure Australia, the federal agency charged with reviewing the nation's infrastructure needs, says the country will need to increase its investments in waste recycling as well as technology such as broadband services and rethink its use of office space due to changes in behaviour during the pandemic.